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 $222.34   8.682%   $241.6436   $241.64   $241.65   $241.60  
  Purchase #2 $23.62   12.607%   $26.5978   $26.60   $26.60   $26.60  
  Purchase #3 $152.75   9.610%   $167.4293   $167.43   $167.45   $167.40  
  Purchase #4 $157.46   6.454%   $167.6225   $167.62   $167.60   $167.60  
  Purchase #5 $250.71   7.529%   $269.586   $269.59   $269.60   $269.60  
  Purchase #6 $93.40   11.528%   $104.1672   $104.17   $104.15   $104.20  
  Purchase #7 $47.94   3.780%   $49.7521   $49.75   $49.75   $49.80  
  7 purchase totals = $948.22       $1,026.7985   $1,026.80   $1,026.80   $1,026.80