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 $48.57   9.638%   $53.2512   $53.25   $53.25   $53.30  
  Purchase #2 $249.97   6.427%   $266.0356   $266.04   $266.05   $266.00  
  Purchase #3 $117.26   5.868%   $124.1408   $124.14   $124.15   $124.10  
  Purchase #4 $250.47   5.416%   $264.0355   $264.04   $264.05   $264.00  
  Purchase #5 $227.69   13.656%   $258.7833   $258.78   $258.80   $258.80  
  Purchase #6 $94.28   6.836%   $100.725   $100.73   $100.75   $100.70  
  Purchase #7 $172.37   4.531%   $180.1801   $180.18   $180.20   $180.20  
  7 purchase totals = $1,160.61       $1,247.1515   $1,247.16   $1,247.25   $1,247.10