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 $230.67   6.619%   $245.938   $245.94   $245.95   $245.90  
  Purchase #2 $191.62   7.344%   $205.6926   $205.69   $205.70   $205.70  
  Purchase #3 $227.33   5.808%   $240.5333   $240.53   $240.55   $240.50  
  Purchase #4 $203.27   10.549%   $224.713   $224.71   $224.70   $224.70  
  Purchase #5 $80.40   5.187%   $84.5703   $84.57   $84.55   $84.60  
  Purchase #6 $183.75   4.750%   $192.4781   $192.48   $192.50   $192.50  
  Purchase #7 $137.96   11.190%   $153.3977   $153.40   $153.40   $153.40  
  7 purchase totals = $1,255.00       $1,347.3230   $1,347.32   $1,347.35   $1,347.30