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 $250.98   10.139%   $276.4269   $276.43   $276.45   $276.40  
  Purchase #2 $95.38   7.822%   $102.8406   $102.84   $102.85   $102.80  
  Purchase #3 $224.90   12.753%   $253.5815   $253.58   $253.60   $253.60  
  Purchase #4 $177.85   12.374%   $199.8572   $199.86   $199.85   $199.90  
  Purchase #5 $67.67   12.592%   $76.191   $76.19   $76.20   $76.20  
  Purchase #6 $94.83   13.431%   $107.5666   $107.57   $107.55   $107.60  
  Purchase #7 $130.73   6.213%   $138.8523   $138.85   $138.85   $138.90  
  7 purchase totals = $1,042.34       $1,155.3161   $1,155.32   $1,155.35   $1,155.40