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 $60.85   8.708%   $66.1488   $66.15   $66.15   $66.10  
  Purchase #2 $221.76   7.749%   $238.9442   $238.94   $238.95   $238.90  
  Purchase #3 $64.59   6.324%   $68.6747   $68.67   $68.65   $68.70  
  Purchase #4 $49.95   3.164%   $51.5304   $51.53   $51.55   $51.50  
  Purchase #5 $214.27   5.467%   $225.9841   $225.98   $226.00   $226.00  
  Purchase #6 $227.45   10.474%   $251.2731   $251.27   $251.25   $251.30  
  Purchase #7 $168.43   7.440%   $180.9612   $180.96   $180.95   $181.00  
  7 purchase totals = $1,007.30       $1,083.5165   $1,083.50   $1,083.50   $1,083.50