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 $243.61   9.301%   $266.2682   $266.27   $266.25   $266.30  
  Purchase #2 $44.82   9.295%   $48.986   $48.99   $49.00   $49.00  
  Purchase #3 $29.61   11.532%   $33.0246   $33.02   $33.00   $33.00  
  Purchase #4 $167.82   9.394%   $183.585   $183.59   $183.60   $183.60  
  Purchase #5 $170.29   6.650%   $181.6143   $181.61   $181.60   $181.60  
  Purchase #6 $125.94   5.401%   $132.742   $132.74   $132.75   $132.70  
  Purchase #7 $18.53   7.612%   $19.9405   $19.94   $19.95   $19.90  
  7 purchase totals = $800.62       $866.1606   $866.16   $866.15   $866.10