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 $200.44   12.830%   $226.1565   $226.16   $226.15   $226.20  
  Purchase #2 $63.94   8.239%   $69.208   $69.21   $69.20   $69.20  
  Purchase #3 $70.76   12.404%   $79.5371   $79.54   $79.55   $79.50  
  Purchase #4 $96.60   7.387%   $103.7358   $103.74   $103.75   $103.70  
  Purchase #5 $37.60   9.519%   $41.1791   $41.18   $41.20   $41.20  
  Purchase #6 $174.37   13.231%   $197.4409   $197.44   $197.45   $197.40  
  Purchase #7 $229.51   6.650%   $244.7724   $244.77   $244.75   $244.80  
  7 purchase totals = $873.22       $962.0298   $962.04   $962.05   $962.00