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 $134.58   12.618%   $151.5613   $151.56   $151.55   $151.60  
  Purchase #2 $55.54   5.783%   $58.7519   $58.75   $58.75   $58.80  
  Purchase #3 $95.87   6.370%   $101.9769   $101.98   $102.00   $102.00  
  Purchase #4 $244.77   7.803%   $263.8694   $263.87   $263.85   $263.90  
  Purchase #5 $224.45   3.619%   $232.5728   $232.57   $232.55   $232.60  
  Purchase #6 $59.36   8.156%   $64.2014   $64.20   $64.20   $64.20  
  Purchase #7 $59.62   5.726%   $63.0338   $63.03   $63.05   $63.00  
  7 purchase totals = $874.19       $935.9675   $935.96   $935.95   $936.10