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 $55.42   5.666%   $58.5601   $58.56   $58.55   $58.60  
  Purchase #2 $45.93   5.171%   $48.305   $48.31   $48.30   $48.30  
  Purchase #3 $114.58   8.663%   $124.5061   $124.51   $124.50   $124.50  
  Purchase #4 $248.98   7.513%   $267.6859   $267.69   $267.70   $267.70  
  Purchase #5 $166.33   8.297%   $180.1304   $180.13   $180.15   $180.10  
  Purchase #6 $250.47   4.291%   $261.2177   $261.22   $261.20   $261.20  
  Purchase #7 $141.54   6.752%   $151.0968   $151.10   $151.10   $151.10  
  7 purchase totals = $1,023.25       $1,091.5020   $1,091.52   $1,091.50   $1,091.50