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 $118.26   12.107%   $132.5777   $132.58   $132.60   $132.60  
  Purchase #2 $199.31   13.147%   $225.5133   $225.51   $225.50   $225.50  
  Purchase #3 $94.27   8.473%   $102.2575   $102.26   $102.25   $102.30  
  Purchase #4 $138.87   3.162%   $143.2611   $143.26   $143.25   $143.30  
  Purchase #5 $24.78   10.204%   $27.3086   $27.31   $27.30   $27.30  
  Purchase #6 $182.53   8.753%   $198.5069   $198.51   $198.50   $198.50  
  Purchase #7 $75.26   8.719%   $81.8219   $81.82   $81.80   $81.80  
  7 purchase totals = $833.28       $911.2470   $911.25   $911.20   $911.30