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 $34.27   8.832%   $37.2967   $37.30   $37.30   $37.30  
  Purchase #2 $188.95   12.735%   $213.0128   $213.01   $213.00   $213.00  
  Purchase #3 $28.96   6.824%   $30.9362   $30.94   $30.95   $30.90  
  Purchase #4 $229.92   7.629%   $247.4606   $247.46   $247.45   $247.50  
  Purchase #5 $241.60   7.562%   $259.8698   $259.87   $259.85   $259.90  
  Purchase #6 $144.39   12.827%   $162.9109   $162.91   $162.90   $162.90  
  Purchase #7 $65.93   12.859%   $74.4079   $74.41   $74.40   $74.40  
  7 purchase totals = $934.02       $1,025.8949   $1,025.90   $1,025.85   $1,025.90