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 $59.36   3.662%   $61.5338   $61.53   $61.55   $61.50  
  Purchase #2 $68.44   10.228%   $75.44   $75.44   $75.45   $75.40  
  Purchase #3 $203.37   12.327%   $228.4394   $228.44   $228.45   $228.40  
  Purchase #4 $117.25   12.698%   $132.1384   $132.14   $132.15   $132.10  
  Purchase #5 $205.36   13.328%   $232.7304   $232.73   $232.75   $232.70  
  Purchase #6 $33.88   12.147%   $37.9954   $38.00   $38.00   $38.00  
  Purchase #7 $196.38   6.430%   $209.0072   $209.01   $209.00   $209.00  
  7 purchase totals = $884.04       $977.2846   $977.29   $977.35   $977.10