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 $34.27   7.201%   $36.7378   $36.74   $36.75   $36.70  
  Purchase #2 $95.32   4.282%   $99.4016   $99.40   $99.40   $99.40  
  Purchase #3 $124.75   9.587%   $136.7098   $136.71   $136.70   $136.70  
  Purchase #4 $83.78   9.288%   $91.5615   $91.56   $91.55   $91.60  
  Purchase #5 $83.67   10.743%   $92.6587   $92.66   $92.65   $92.70  
  Purchase #6 $229.50   7.110%   $245.8175   $245.82   $245.80   $245.80  
  Purchase #7 $240.42   5.659%   $254.0254   $254.03   $254.05   $254.00  
  7 purchase totals = $891.71       $956.9123   $956.92   $956.90   $956.90