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 $46.75   11.230%   $52   $52.00   $52.00   $52.00  
  Purchase #2 $204.81   13.160%   $231.763   $231.76   $231.75   $231.80  
  Purchase #3 $34.68   13.209%   $39.2609   $39.26   $39.25   $39.30  
  Purchase #4 $6.48   11.326%   $7.2139   $7.21   $7.20   $7.20  
  Purchase #5 $125.42   10.832%   $139.0055   $139.01   $139.00   $139.00  
  Purchase #6 $98.33   4.557%   $102.8109   $102.81   $102.80   $102.80  
  Purchase #7 $175.33   8.831%   $190.8134   $190.81   $190.80   $190.80  
  7 purchase totals = $691.80       $762.8676   $762.86   $762.80   $762.90