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 $89.44   5.706%   $94.5434   $94.54   $94.55   $94.50  
  Purchase #2 $23.67   11.222%   $26.3262   $26.33   $26.35   $26.30  
  Purchase #3 $174.71   5.350%   $184.057   $184.06   $184.05   $184.10  
  Purchase #4 $180.30   10.417%   $199.0819   $199.08   $199.10   $199.10  
  Purchase #5 $170.78   10.159%   $188.1295   $188.13   $188.15   $188.10  
  Purchase #6 $215.28   8.602%   $233.7984   $233.80   $233.80   $233.80  
  Purchase #7 $58.61   4.114%   $61.0212   $61.02   $61.00   $61.00  
  7 purchase totals = $912.79       $986.9576   $986.96   $987.00   $986.90