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 $40.33   13.563%   $45.8   $45.80   $45.80   $45.80  
  Purchase #2 $119.38   4.671%   $124.9562   $124.96   $124.95   $125.00  
  Purchase #3 $12.83   4.156%   $13.3632   $13.36   $13.35   $13.40  
  Purchase #4 $27.86   5.232%   $29.3176   $29.32   $29.30   $29.30  
  Purchase #5 $144.98   11.393%   $161.4976   $161.50   $161.50   $161.50  
  Purchase #6 $203.55   4.102%   $211.8996   $211.90   $211.90   $211.90  
  Purchase #7 $18.68   11.498%   $20.8278   $20.83   $20.85   $20.80  
  7 purchase totals = $567.61       $607.6620   $607.67   $607.65   $607.70