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 $60.85   13.684%   $69.1767   $69.18   $69.20   $69.20  
  Purchase #2 $223.56   11.667%   $249.6427   $249.64   $249.65   $249.60  
  Purchase #3 $206.48   7.113%   $221.1669   $221.17   $221.15   $221.20  
  Purchase #4 $47.32   9.350%   $51.7444   $51.74   $51.75   $51.70  
  Purchase #5 $178.48   4.376%   $186.2903   $186.29   $186.30   $186.30  
  Purchase #6 $172.97   5.496%   $182.4764   $182.48   $182.50   $182.50  
  Purchase #7 $81.79   11.761%   $91.4093   $91.41   $91.40   $91.40  
  7 purchase totals = $971.45       $1,051.9067   $1,051.91   $1,051.95   $1,051.90