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 $44.25   7.295%   $47.478   $47.48   $47.50   $47.50  
  Purchase #2 $222.51   9.519%   $243.6907   $243.69   $243.70   $243.70  
  Purchase #3 $246.67   3.813%   $256.0755   $256.08   $256.10   $256.10  
  Purchase #4 $203.76   6.177%   $216.3463   $216.35   $216.35   $216.30  
  Purchase #5 $59.65   5.192%   $62.747   $62.75   $62.75   $62.70  
  Purchase #6 $26.37   4.389%   $27.5274   $27.53   $27.55   $27.50  
  Purchase #7 $23.51   7.443%   $25.2598   $25.26   $25.25   $25.30  
  7 purchase totals = $826.72       $879.1247   $879.14   $879.20   $879.10