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 $250.26   5.748%   $264.6449   $264.64   $264.65   $264.60  
  Purchase #2 $204.32   10.753%   $226.2905   $226.29   $226.30   $226.30  
  Purchase #3 $162.68   3.264%   $167.9899   $167.99   $168.00   $168.00  
  Purchase #4 $125.82   9.198%   $137.3929   $137.39   $137.40   $137.40  
  Purchase #5 $194.88   4.828%   $204.2888   $204.29   $204.30   $204.30  
  Purchase #6 $174.93   8.346%   $189.5297   $189.53   $189.55   $189.50  
  Purchase #7 $68.26   7.674%   $73.4983   $73.50   $73.50   $73.50  
  7 purchase totals = $1,181.15       $1,263.6350   $1,263.63   $1,263.70   $1,263.60