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 $61.32   12.732%   $69.1273   $69.13   $69.15   $69.10  
  Purchase #2 $81.66   7.845%   $88.0662   $88.07   $88.05   $88.10  
  Purchase #3 $147.39   10.579%   $162.9824   $162.98   $163.00   $163.00  
  Purchase #4 $106.34   9.468%   $116.4083   $116.41   $116.40   $116.40  
  Purchase #5 $172.43   10.541%   $190.6058   $190.61   $190.60   $190.60  
  Purchase #6 $134.35   13.799%   $152.889   $152.89   $152.90   $152.90  
  Purchase #7 $161.79   5.634%   $170.9052   $170.91   $170.90   $170.90  
  7 purchase totals = $865.28       $950.9842   $951.00   $951.00   $951.00