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 $59.80   3.632%   $61.9719   $61.97   $61.95   $62.00  
  Purchase #2 $33.97   5.755%   $35.925   $35.93   $35.95   $35.90  
  Purchase #3 $65.90   5.173%   $69.309   $69.31   $69.30   $69.30  
  Purchase #4 $240.43   4.242%   $250.629   $250.63   $250.65   $250.60  
  Purchase #5 $160.82   10.781%   $178.158   $178.16   $178.15   $178.20  
  Purchase #6 $170.36   9.690%   $186.8679   $186.87   $186.85   $186.90  
  Purchase #7 $61.88   6.746%   $66.0544   $66.05   $66.05   $66.10  
  7 purchase totals = $793.16       $848.9152   $848.92   $848.90   $849.00