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 $239.26   11.682%   $267.2104   $267.21   $267.20   $267.20  
  Purchase #2 $200.27   13.213%   $226.7317   $226.73   $226.75   $226.70  
  Purchase #3 $59.41   6.422%   $63.2253   $63.23   $63.25   $63.20  
  Purchase #4 $250.46   5.390%   $263.9598   $263.96   $263.95   $264.00  
  Purchase #5 $113.62   12.606%   $127.9429   $127.94   $127.95   $127.90  
  Purchase #6 $29.96   7.178%   $32.1105   $32.11   $32.10   $32.10  
  Purchase #7 $137.71   11.457%   $153.4874   $153.49   $153.50   $153.50  
  7 purchase totals = $1,030.69       $1,134.6680   $1,134.67   $1,134.70   $1,134.60