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 $248.51   5.413%   $261.9618   $261.96   $261.95   $262.00  
  Purchase #2 $132.74   5.859%   $140.5172   $140.52   $140.50   $140.50  
  Purchase #3 $209.39   5.601%   $221.1179   $221.12   $221.10   $221.10  
  Purchase #4 $56.54   8.831%   $61.533   $61.53   $61.55   $61.50  
  Purchase #5 $84.80   6.521%   $90.3298   $90.33   $90.35   $90.30  
  Purchase #6 $60.25   7.202%   $64.5892   $64.59   $64.60   $64.60  
  Purchase #7 $113.46   6.699%   $121.0607   $121.06   $121.05   $121.10  
  7 purchase totals = $905.69       $961.1096   $961.11   $961.10   $961.10