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 $82.47   11.498%   $91.9524   $91.95   $91.95   $92.00  
  Purchase #2 $52.29   13.123%   $59.152   $59.15   $59.15   $59.20  
  Purchase #3 $88.63   5.392%   $93.4089   $93.41   $93.40   $93.40  
  Purchase #4 $63.89   10.416%   $70.5448   $70.54   $70.55   $70.50  
  Purchase #5 $6.83   5.592%   $7.2119   $7.21   $7.20   $7.20  
  Purchase #6 $124.75   9.106%   $136.1097   $136.11   $136.10   $136.10  
  Purchase #7 $165.30   6.534%   $176.1007   $176.10   $176.10   $176.10  
  7 purchase totals = $584.16       $634.4804   $634.47   $634.45   $634.50