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 $200.33   13.233%   $226.8397   $226.84   $226.85   $226.80  
  Purchase #2 $159.74   9.751%   $175.3162   $175.32   $175.30   $175.30  
  Purchase #3 $19.96   9.734%   $21.9029   $21.90   $21.90   $21.90  
  Purchase #4 $244.59   12.308%   $274.6941   $274.69   $274.70   $274.70  
  Purchase #5 $54.80   10.109%   $60.3397   $60.34   $60.35   $60.30  
  Purchase #6 $188.86   6.804%   $201.71   $201.71   $201.70   $201.70  
  Purchase #7 $250.50   12.816%   $282.6041   $282.60   $282.60   $282.60  
  7 purchase totals = $1,118.78       $1,243.4067   $1,243.40   $1,243.40   $1,243.30