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 $168.94   8.660%   $183.5702   $183.57   $183.55   $183.60  
  Purchase #2 $110.57   10.205%   $121.8537   $121.85   $121.85   $121.90  
  Purchase #3 $67.48   10.835%   $74.7915   $74.79   $74.80   $74.80  
  Purchase #4 $223.93   13.371%   $253.8717   $253.87   $253.85   $253.90  
  Purchase #5 $187.99   5.596%   $198.5099   $198.51   $198.50   $198.50  
  Purchase #6 $138.97   13.303%   $157.4572   $157.46   $157.45   $157.50  
  Purchase #7 $55.64   6.601%   $59.3128   $59.31   $59.30   $59.30  
  7 purchase totals = $953.52       $1,049.3670   $1,049.36   $1,049.30   $1,049.50