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 $177.74   5.765%   $187.9867   $187.99   $188.00   $188.00  
  Purchase #2 $125.45   9.831%   $137.783   $137.78   $137.80   $137.80  
  Purchase #3 $81.45   11.150%   $90.5317   $90.53   $90.55   $90.50  
  Purchase #4 $94.62   10.244%   $104.3129   $104.31   $104.30   $104.30  
  Purchase #5 $127.25   3.850%   $132.1491   $132.15   $132.15   $132.10  
  Purchase #6 $161.86   5.519%   $170.7931   $170.79   $170.80   $170.80  
  Purchase #7 $50.52   7.598%   $54.3585   $54.36   $54.35   $54.40  
  7 purchase totals = $818.89       $877.9150   $877.91   $877.95   $877.90