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 $97.81   4.566%   $102.276   $102.28   $102.30   $102.30  
  Purchase #2 $235.87   8.467%   $255.8411   $255.84   $255.85   $255.80  
  Purchase #3 $15.52   8.193%   $16.7916   $16.79   $16.80   $16.80  
  Purchase #4 $149.74   5.514%   $157.9967   $158.00   $158.00   $158.00  
  Purchase #5 $186.43   10.354%   $205.733   $205.73   $205.75   $205.70  
  Purchase #6 $195.39   10.547%   $215.9978   $216.00   $216.00   $216.00  
  Purchase #7 $236.44   8.156%   $255.724   $255.72   $255.70   $255.70  
  7 purchase totals = $1,117.20       $1,210.3602   $1,210.36   $1,210.40   $1,210.30