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 $196.86   9.573%   $215.7054   $215.71   $215.70   $215.70  
  Purchase #2 $54.57   11.860%   $61.042   $61.04   $61.05   $61.00  
  Purchase #3 $28.66   5.253%   $30.1655   $30.17   $30.15   $30.20  
  Purchase #4 $34.71   13.489%   $39.392   $39.39   $39.40   $39.40  
  Purchase #5 $182.51   10.588%   $201.8342   $201.83   $201.85   $201.80  
  Purchase #6 $152.44   5.862%   $161.376   $161.38   $161.40   $161.40  
  Purchase #7 $216.97   12.369%   $243.807   $243.81   $243.80   $243.80  
  7 purchase totals = $866.72       $953.3221   $953.33   $953.35   $953.30