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 $57.98   12.161%   $65.0309   $65.03   $65.05   $65.00  
  Purchase #2 $231.62   9.404%   $253.4015   $253.40   $253.40   $253.40  
  Purchase #3 $163.59   13.640%   $185.9037   $185.90   $185.90   $185.90  
  Purchase #4 $146.84   8.666%   $159.5652   $159.57   $159.55   $159.60  
  Purchase #5 $148.64   10.265%   $163.8979   $163.90   $163.90   $163.90  
  Purchase #6 $214.91   7.401%   $230.8155   $230.82   $230.80   $230.80  
  Purchase #7 $231.49   4.430%   $241.745   $241.75   $241.75   $241.70  
  7 purchase totals = $1,195.07       $1,300.3597   $1,300.37   $1,300.35   $1,300.30