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 $163.31   7.122%   $174.9409   $174.94   $174.95   $174.90  
  Purchase #2 $176.44   13.477%   $200.2188   $200.22   $200.20   $200.20  
  Purchase #3 $69.58   10.499%   $76.8852   $76.89   $76.90   $76.90  
  Purchase #4 $250.91   6.558%   $267.3647   $267.36   $267.35   $267.40  
  Purchase #5 $32.54   8.790%   $35.4003   $35.40   $35.40   $35.40  
  Purchase #6 $189.58   5.828%   $200.6287   $200.63   $200.65   $200.60  
  Purchase #7 $69.32   3.384%   $71.6658   $71.67   $71.65   $71.70  
  7 purchase totals = $951.68       $1,027.1044   $1,027.11   $1,027.10   $1,027.10