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 $200.98   12.708%   $226.5205   $226.52   $226.50   $226.50  
  Purchase #2 $136.96   9.794%   $150.3739   $150.37   $150.35   $150.40  
  Purchase #3 $101.76   7.479%   $109.3706   $109.37   $109.35   $109.40  
  Purchase #4 $66.89   6.384%   $71.1603   $71.16   $71.15   $71.20  
  Purchase #5 $119.67   4.619%   $125.1976   $125.20   $125.20   $125.20  
  Purchase #6 $229.87   5.295%   $242.0416   $242.04   $242.05   $242.00  
  Purchase #7 $120.58   12.154%   $135.2353   $135.24   $135.25   $135.20  
  7 purchase totals = $976.71       $1,059.8998   $1,059.90   $1,059.85   $1,059.90