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 $247.95   11.691%   $276.9378   $276.94   $276.95   $276.90  
  Purchase #2 $243.51   3.819%   $252.8096   $252.81   $252.80   $252.80  
  Purchase #3 $126.40   10.743%   $139.9792   $139.98   $140.00   $140.00  
  Purchase #4 $156.73   5.712%   $165.6824   $165.68   $165.70   $165.70  
  Purchase #5 $83.78   3.872%   $87.024   $87.02   $87.00   $87.00  
  Purchase #6 $181.78   9.854%   $199.6926   $199.69   $199.70   $199.70  
  Purchase #7 $95.67   8.675%   $103.9694   $103.97   $103.95   $104.00  
  7 purchase totals = $1,135.82       $1,226.0950   $1,226.09   $1,226.10   $1,226.10