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 $250.65   5.624%   $264.7466   $264.75   $264.75   $264.70  
  Purchase #2 $57.43   4.468%   $59.996   $60.00   $60.00   $60.00  
  Purchase #3 $99.95   13.254%   $113.1974   $113.20   $113.20   $113.20  
  Purchase #4 $189.91   5.806%   $200.9362   $200.94   $200.95   $200.90  
  Purchase #5 $49.90   3.834%   $51.8132   $51.81   $51.80   $51.80  
  Purchase #6 $195.42   6.547%   $208.2141   $208.21   $208.20   $208.20  
  Purchase #7 $112.91   3.310%   $116.6473   $116.65   $116.65   $116.60  
  7 purchase totals = $956.17       $1,015.5508   $1,015.56   $1,015.55   $1,015.40