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 $44.97   5.675%   $47.522   $47.52   $47.50   $47.50  
  Purchase #2 $7.39   12.791%   $8.3353   $8.34   $8.35   $8.30  
  Purchase #3 $201.36   5.695%   $212.8275   $212.83   $212.85   $212.80  
  Purchase #4 $91.35   7.467%   $98.1711   $98.17   $98.15   $98.20  
  Purchase #5 $114.97   5.344%   $121.114   $121.11   $121.10   $121.10  
  Purchase #6 $59.51   11.813%   $66.5399   $66.54   $66.55   $66.50  
  Purchase #7 $250.61   9.813%   $275.2024   $275.20   $275.20   $275.20  
  7 purchase totals = $770.16       $829.7122   $829.71   $829.70   $829.60