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 $197.95   13.417%   $224.509   $224.51   $224.50   $224.50  
  Purchase #2 $249.39   10.529%   $275.6483   $275.65   $275.65   $275.60  
  Purchase #3 $236.26   6.490%   $251.5933   $251.59   $251.60   $251.60  
  Purchase #4 $91.94   4.158%   $95.7629   $95.76   $95.75   $95.80  
  Purchase #5 $12.41   9.492%   $13.588   $13.59   $13.60   $13.60  
  Purchase #6 $214.82   4.648%   $224.8048   $224.80   $224.80   $224.80  
  Purchase #7 $117.34   5.330%   $123.5942   $123.59   $123.60   $123.60  
  7 purchase totals = $1,120.11       $1,209.5005   $1,209.49   $1,209.50   $1,209.50