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 $191.30   11.841%   $213.9518   $213.95   $213.95   $214.00  
  Purchase #2 $40.50   13.682%   $46.0412   $46.04   $46.05   $46.00  
  Purchase #3 $246.51   12.646%   $277.6837   $277.68   $277.70   $277.70  
  Purchase #4 $212.84   6.804%   $227.3216   $227.32   $227.30   $227.30  
  Purchase #5 $249.66   8.712%   $271.4104   $271.41   $271.40   $271.40  
  Purchase #6 $84.93   13.612%   $96.4907   $96.49   $96.50   $96.50  
  Purchase #7 $20.27   9.296%   $22.1543   $22.15   $22.15   $22.20  
  7 purchase totals = $1,046.01       $1,155.0537   $1,155.04   $1,155.05   $1,155.10