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 $204.71   3.269%   $211.402   $211.40   $211.40   $211.40  
  Purchase #2 $84.87   12.873%   $95.7953   $95.80   $95.80   $95.80  
  Purchase #3 $175.89   10.671%   $194.6592   $194.66   $194.65   $194.70  
  Purchase #4 $156.43   9.679%   $171.5709   $171.57   $171.55   $171.60  
  Purchase #5 $93.75   12.656%   $105.615   $105.62   $105.60   $105.60  
  Purchase #6 $28.61   10.328%   $31.5648   $31.56   $31.55   $31.60  
  Purchase #7 $115.57   8.141%   $124.9786   $124.98   $125.00   $125.00  
  7 purchase totals = $859.83       $935.5858   $935.59   $935.55   $935.70