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 $186.94   11.203%   $207.8829   $207.88   $207.90   $207.90  
  Purchase #2 $170.51   12.797%   $192.3302   $192.33   $192.35   $192.30  
  Purchase #3 $12.76   11.290%   $14.2006   $14.20   $14.20   $14.20  
  Purchase #4 $116.56   10.813%   $129.1636   $129.16   $129.15   $129.20  
  Purchase #5 $168.90   7.138%   $180.9561   $180.96   $180.95   $181.00  
  Purchase #6 $234.65   4.279%   $244.6907   $244.69   $244.70   $244.70  
  Purchase #7 $162.77   12.181%   $182.597   $182.60   $182.60   $182.60  
  7 purchase totals = $1,053.09       $1,151.8211   $1,151.82   $1,151.85   $1,151.90