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 $81.52   13.562%   $92.5757   $92.58   $92.60   $92.60  
  Purchase #2 $59.77   4.630%   $62.5374   $62.54   $62.55   $62.50  
  Purchase #3 $222.82   8.636%   $242.0627   $242.06   $242.05   $242.10  
  Purchase #4 $50.34   5.856%   $53.2879   $53.29   $53.30   $53.30  
  Purchase #5 $39.57   5.138%   $41.6031   $41.60   $41.60   $41.60  
  Purchase #6 $220.66   4.580%   $230.7662   $230.77   $230.75   $230.80  
  Purchase #7 $97.30   4.327%   $101.5102   $101.51   $101.50   $101.50  
  7 purchase totals = $771.98       $824.3432   $824.35   $824.35   $824.40