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 $204.48   10.341%   $225.6253   $225.63   $225.65   $225.60  
  Purchase #2 $44.40   5.353%   $46.7767   $46.78   $46.80   $46.80  
  Purchase #3 $219.85   5.489%   $231.9176   $231.92   $231.90   $231.90  
  Purchase #4 $239.83   4.172%   $249.8357   $249.84   $249.85   $249.80  
  Purchase #5 $243.41   6.624%   $259.5335   $259.53   $259.55   $259.50  
  Purchase #6 $17.29   11.501%   $19.2785   $19.28   $19.30   $19.30  
  Purchase #7 $230.37   4.809%   $241.4485   $241.45   $241.45   $241.40  
  7 purchase totals = $1,199.63       $1,274.4158   $1,274.43   $1,274.50   $1,274.30