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 $185.98   12.259%   $208.7793   $208.78   $208.80   $208.80  
  Purchase #2 $54.89   11.149%   $61.0097   $61.01   $61.00   $61.00  
  Purchase #3 $204.70   9.664%   $224.4822   $224.48   $224.50   $224.50  
  Purchase #4 $81.44   5.619%   $86.0161   $86.02   $86.00   $86.00  
  Purchase #5 $217.66   5.176%   $228.9261   $228.93   $228.95   $228.90  
  Purchase #6 $122.66   10.221%   $135.1971   $135.20   $135.20   $135.20  
  Purchase #7 $85.39   9.165%   $93.216   $93.22   $93.20   $93.20  
  7 purchase totals = $952.72       $1,037.6265   $1,037.64   $1,037.65   $1,037.60