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 $42.53   9.568%   $46.5993   $46.60   $46.60   $46.60  
  Purchase #2 $88.96   4.329%   $92.8111   $92.81   $92.80   $92.80  
  Purchase #3 $221.44   3.812%   $229.8813   $229.88   $229.90   $229.90  
  Purchase #4 $188.58   8.625%   $204.845   $204.85   $204.85   $204.80  
  Purchase #5 $184.43   11.347%   $205.3573   $205.36   $205.35   $205.40  
  Purchase #6 $169.93   5.378%   $179.0688   $179.07   $179.05   $179.10  
  Purchase #7 $31.55   11.159%   $35.0707   $35.07   $35.05   $35.10  
  7 purchase totals = $927.42       $993.6335   $993.64   $993.60   $993.70