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 $192.93   6.409%   $205.2949   $205.29   $205.30   $205.30  
  Purchase #2 $231.86   9.246%   $253.2978   $253.30   $253.30   $253.30  
  Purchase #3 $217.90   10.400%   $240.5616   $240.56   $240.55   $240.60  
  Purchase #4 $222.39   10.768%   $246.337   $246.34   $246.35   $246.30  
  Purchase #5 $97.42   8.346%   $105.5507   $105.55   $105.55   $105.60  
  Purchase #6 $57.64   4.207%   $60.0649   $60.06   $60.05   $60.10  
  Purchase #7 $102.58   5.846%   $108.5768   $108.58   $108.60   $108.60  
  7 purchase totals = $1,122.72       $1,219.6837   $1,219.68   $1,219.70   $1,219.80