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 $97.30   5.106%   $102.2681   $102.27   $102.25   $102.30  
  Purchase #2 $75.82   7.711%   $81.6665   $81.67   $81.65   $81.70  
  Purchase #3 $149.28   6.793%   $159.4206   $159.42   $159.40   $159.40  
  Purchase #4 $210.45   6.612%   $224.365   $224.37   $224.35   $224.40  
  Purchase #5 $143.34   6.698%   $152.9409   $152.94   $152.95   $152.90  
  Purchase #6 $80.53   7.297%   $86.4063   $86.41   $86.40   $86.40  
  Purchase #7 $212.77   6.572%   $226.7532   $226.75   $226.75   $226.80  
  7 purchase totals = $969.49       $1,033.8206   $1,033.83   $1,033.75   $1,033.90