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 $188.35   3.295%   $194.5561   $194.56   $194.55   $194.60  
  Purchase #2 $231.39   10.583%   $255.878   $255.88   $255.90   $255.90  
  Purchase #3 $129.59   10.364%   $143.0207   $143.02   $143.00   $143.00  
  Purchase #4 $96.50   5.701%   $102.0015   $102.00   $102.00   $102.00  
  Purchase #5 $189.78   8.445%   $205.8069   $205.81   $205.80   $205.80  
  Purchase #6 $69.66   8.490%   $75.5741   $75.57   $75.55   $75.60  
  Purchase #7 $248.85   3.180%   $256.7634   $256.76   $256.75   $256.80  
  7 purchase totals = $1,154.12       $1,233.6007   $1,233.60   $1,233.55   $1,233.70