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 $209.33   11.218%   $232.8126   $232.81   $232.80   $232.80  
  Purchase #2 $118.30   12.394%   $132.9621   $132.96   $132.95   $133.00  
  Purchase #3 $145.78   4.274%   $152.0106   $152.01   $152.00   $152.00  
  Purchase #4 $97.29   4.129%   $101.3071   $101.31   $101.30   $101.30  
  Purchase #5 $95.48   11.646%   $106.5996   $106.60   $106.60   $106.60  
  Purchase #6 $71.39   13.289%   $80.877   $80.88   $80.90   $80.90  
  Purchase #7 $82.33   4.872%   $86.3411   $86.34   $86.35   $86.30  
  7 purchase totals = $819.90       $892.9101   $892.91   $892.90   $892.90