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 $180.63   12.304%   $202.8547   $202.85   $202.85   $202.90  
  Purchase #2 $104.77   6.499%   $111.579   $111.58   $111.60   $111.60  
  Purchase #3 $67.49   11.355%   $75.1535   $75.15   $75.15   $75.20  
  Purchase #4 $216.25   13.157%   $244.702   $244.70   $244.70   $244.70  
  Purchase #5 $138.61   13.783%   $157.7146   $157.71   $157.70   $157.70  
  Purchase #6 $246.96   6.560%   $263.1606   $263.16   $263.15   $263.20  
  Purchase #7 $197.32   7.242%   $211.6099   $211.61   $211.60   $211.60  
  7 purchase totals = $1,152.03       $1,266.7743   $1,266.76   $1,266.75   $1,266.90