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 $23.47   13.862%   $26.7234   $26.72   $26.70   $26.70  
  Purchase #2 $189.39   6.504%   $201.7079   $201.71   $201.70   $201.70  
  Purchase #3 $133.60   11.740%   $149.2846   $149.28   $149.30   $149.30  
  Purchase #4 $39.65   5.388%   $41.7863   $41.79   $41.80   $41.80  
  Purchase #5 $49.35   11.538%   $55.044   $55.04   $55.05   $55.00  
  Purchase #6 $185.69   5.272%   $195.4796   $195.48   $195.50   $195.50  
  Purchase #7 $176.55   10.277%   $194.694   $194.69   $194.70   $194.70  
  7 purchase totals = $797.70       $864.7198   $864.71   $864.75   $864.70