Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $242.52   13.560%   $275.4057   $275.41   $275.40   $275.40  
  Purchase #2 $214.90   12.576%   $241.9258   $241.93   $241.95   $241.90  
  Purchase #3 $156.29   9.449%   $171.0578   $171.06   $171.05   $171.10  
  Purchase #4 $239.79   7.534%   $257.8558   $257.86   $257.85   $257.90  
  Purchase #5 $188.99   3.348%   $195.3174   $195.32   $195.30   $195.30  
  Purchase #6 $190.60   4.326%   $198.8454   $198.85   $198.85   $198.80  
  Purchase #7 $112.98   6.684%   $120.5316   $120.53   $120.55   $120.50  
  7 purchase totals = $1,346.07       $1,460.9395   $1,460.96   $1,460.95   $1,460.90