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 $236.57   3.298%   $244.3721   $244.37   $244.35   $244.40  
  Purchase #2 $22.51   4.803%   $23.5912   $23.59   $23.60   $23.60  
  Purchase #3 $66.39   4.505%   $69.3809   $69.38   $69.40   $69.40  
  Purchase #4 $6.52   11.635%   $7.2786   $7.28   $7.30   $7.30  
  Purchase #5 $17.71   3.288%   $18.2923   $18.29   $18.30   $18.30  
  Purchase #6 $216.76   12.522%   $243.9027   $243.90   $243.90   $243.90  
  Purchase #7 $230.47   10.570%   $254.8307   $254.83   $254.85   $254.80  
  7 purchase totals = $796.93       $861.6485   $861.64   $861.70   $861.70