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 $131.53   11.442%   $146.5797   $146.58   $146.60   $146.60  
  Purchase #2 $69.79   3.702%   $72.3736   $72.37   $72.35   $72.40  
  Purchase #3 $141.80   8.847%   $154.345   $154.35   $154.35   $154.30  
  Purchase #4 $38.43   9.838%   $42.2107   $42.21   $42.20   $42.20  
  Purchase #5 $188.43   3.474%   $194.9761   $194.98   $195.00   $195.00  
  Purchase #6 $95.63   3.557%   $99.0316   $99.03   $99.05   $99.00  
  Purchase #7 $45.41   6.305%   $48.2731   $48.27   $48.25   $48.30  
  7 purchase totals = $711.02       $757.7898   $757.79   $757.80   $757.80