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 $205.83   3.118%   $212.2478   $212.25   $212.25   $212.20  
  Purchase #2 $61.98   7.613%   $66.6985   $66.70   $66.70   $66.70  
  Purchase #3 $193.45   8.188%   $209.2897   $209.29   $209.30   $209.30  
  Purchase #4 $229.69   7.256%   $246.3563   $246.36   $246.35   $246.40  
  Purchase #5 $220.31   10.178%   $242.7332   $242.73   $242.75   $242.70  
  Purchase #6 $61.76   8.483%   $66.9991   $67.00   $67.00   $67.00  
  Purchase #7 $244.38   7.821%   $263.493   $263.49   $263.50   $263.50  
  7 purchase totals = $1,217.40       $1,307.8176   $1,307.82   $1,307.85   $1,307.80