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 $185.88   11.844%   $207.8956   $207.90   $207.90   $207.90  
  Purchase #2 $189.90   10.574%   $209.98   $209.98   $210.00   $210.00  
  Purchase #3 $87.64   7.599%   $94.2998   $94.30   $94.30   $94.30  
  Purchase #4 $53.28   10.349%   $58.7939   $58.79   $58.80   $58.80  
  Purchase #5 $110.74   11.172%   $123.1119   $123.11   $123.10   $123.10  
  Purchase #6 $134.90   13.756%   $153.4568   $153.46   $153.45   $153.50  
  Purchase #7 $122.60   4.553%   $128.182   $128.18   $128.20   $128.20  
  7 purchase totals = $884.94       $975.7200   $975.72   $975.75   $975.80