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 $160.41   13.771%   $182.5001   $182.50   $182.50   $182.50  
  Purchase #2 $242.46   11.768%   $270.9927   $270.99   $271.00   $271.00  
  Purchase #3 $67.97   6.320%   $72.2657   $72.27   $72.25   $72.30  
  Purchase #4 $236.85   5.637%   $250.2012   $250.20   $250.20   $250.20  
  Purchase #5 $171.82   6.125%   $182.344   $182.34   $182.35   $182.30  
  Purchase #6 $228.31   4.333%   $238.2027   $238.20   $238.20   $238.20  
  Purchase #7 $239.78   8.576%   $260.3435   $260.34   $260.35   $260.30  
  7 purchase totals = $1,347.60       $1,456.8499   $1,456.84   $1,456.85   $1,456.80