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 $131.79   3.197%   $136.0033   $136.00   $136.00   $136.00  
  Purchase #2 $68.64   9.672%   $75.2789   $75.28   $75.30   $75.30  
  Purchase #3 $193.85   5.431%   $204.378   $204.38   $204.40   $204.40  
  Purchase #4 $150.81   12.856%   $170.1981   $170.20   $170.20   $170.20  
  Purchase #5 $58.46   3.867%   $60.7206   $60.72   $60.70   $60.70  
  Purchase #6 $83.54   13.463%   $94.787   $94.79   $94.80   $94.80  
  Purchase #7 $86.39   8.411%   $93.6563   $93.66   $93.65   $93.70  
  7 purchase totals = $773.48       $835.0222   $835.03   $835.05   $835.10