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 $250.34   7.272%   $268.5447   $268.54   $268.55   $268.50  
  Purchase #2 $53.85   8.555%   $58.4569   $58.46   $58.45   $58.50  
  Purchase #3 $224.73   3.679%   $232.9978   $233.00   $233.00   $233.00  
  Purchase #4 $153.88   4.226%   $160.383   $160.38   $160.40   $160.40  
  Purchase #5 $231.66   6.354%   $246.3797   $246.38   $246.40   $246.40  
  Purchase #6 $89.62   11.782%   $100.179   $100.18   $100.20   $100.20  
  Purchase #7 $102.96   12.508%   $115.8382   $115.84   $115.85   $115.80  
  7 purchase totals = $1,107.04       $1,182.7793   $1,182.78   $1,182.85   $1,182.80