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 $57.83   9.776%   $63.4835   $63.48   $63.50   $63.50  
  Purchase #2 $243.69   6.681%   $259.9709   $259.97   $259.95   $260.00  
  Purchase #3 $166.26   9.706%   $182.3972   $182.40   $182.40   $182.40  
  Purchase #4 $156.64   9.524%   $171.5584   $171.56   $171.55   $171.60  
  Purchase #5 $150.96   7.434%   $162.1824   $162.18   $162.20   $162.20  
  Purchase #6 $228.32   7.503%   $245.4508   $245.45   $245.45   $245.50  
  Purchase #7 $69.78   13.221%   $79.0056   $79.01   $79.00   $79.00  
  7 purchase totals = $1,073.48       $1,164.0488   $1,164.05   $1,164.05   $1,164.20