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 $20.43   5.109%   $21.4738   $21.47   $21.45   $21.50  
  Purchase #2 $174.70   5.220%   $183.8193   $183.82   $183.80   $183.80  
  Purchase #3 $213.82   3.689%   $221.7078   $221.71   $221.70   $221.70  
  Purchase #4 $51.27   8.289%   $55.5198   $55.52   $55.50   $55.50  
  Purchase #5 $159.81   10.321%   $176.304   $176.30   $176.30   $176.30  
  Purchase #6 $82.64   11.464%   $92.1138   $92.11   $92.10   $92.10  
  Purchase #7 $120.80   3.172%   $124.6318   $124.63   $124.65   $124.60  
  7 purchase totals = $823.47       $875.5703   $875.56   $875.50   $875.50