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 $61.40   7.826%   $66.2052   $66.21   $66.20   $66.20  
  Purchase #2 $212.95   11.219%   $236.8409   $236.84   $236.85   $236.80  
  Purchase #3 $198.92   12.600%   $223.9839   $223.98   $224.00   $224.00  
  Purchase #4 $10.45   10.338%   $11.5303   $11.53   $11.55   $11.50  
  Purchase #5 $82.50   10.745%   $91.3646   $91.36   $91.35   $91.40  
  Purchase #6 $99.29   8.212%   $107.4437   $107.44   $107.45   $107.40  
  Purchase #7 $64.58   3.755%   $67.005   $67.01   $67.00   $67.00  
  7 purchase totals = $730.09       $804.3736   $804.37   $804.40   $804.30