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 $60.55   8.186%   $65.5066   $65.51   $65.50   $65.50  
  Purchase #2 $250.94   12.629%   $282.6312   $282.63   $282.65   $282.60  
  Purchase #3 $19.29   8.662%   $20.9609   $20.96   $20.95   $21.00  
  Purchase #4 $96.29   9.413%   $105.3538   $105.35   $105.35   $105.40  
  Purchase #5 $196.28   10.535%   $216.9581   $216.96   $216.95   $217.00  
  Purchase #6 $133.49   5.127%   $140.334   $140.33   $140.35   $140.30  
  Purchase #7 $170.32   7.183%   $182.5541   $182.55   $182.55   $182.60  
  7 purchase totals = $927.16       $1,014.2987   $1,014.29   $1,014.30   $1,014.40