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 $76.41   9.657%   $83.7889   $83.79   $83.80   $83.80  
  Purchase #2 $109.94   3.873%   $114.198   $114.20   $114.20   $114.20  
  Purchase #3 $18.36   7.221%   $19.6858   $19.69   $19.70   $19.70  
  Purchase #4 $25.48   4.108%   $26.5267   $26.53   $26.55   $26.50  
  Purchase #5 $187.66   3.871%   $194.9243   $194.92   $194.90   $194.90  
  Purchase #6 $5.65   13.813%   $6.4304   $6.43   $6.45   $6.40  
  Purchase #7 $111.56   9.271%   $121.9027   $121.90   $121.90   $121.90  
  7 purchase totals = $535.06       $567.4568   $567.46   $567.50   $567.40