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 $208.39   9.302%   $227.7744   $227.77   $227.75   $227.80  
  Purchase #2 $208.71   10.224%   $230.0485   $230.05   $230.05   $230.00  
  Purchase #3 $102.56   13.160%   $116.0569   $116.06   $116.05   $116.10  
  Purchase #4 $152.32   6.727%   $162.5666   $162.57   $162.55   $162.60  
  Purchase #5 $32.98   3.665%   $34.1887   $34.19   $34.20   $34.20  
  Purchase #6 $83.39   9.717%   $91.493   $91.49   $91.50   $91.50  
  Purchase #7 $144.39   4.697%   $151.172   $151.17   $151.15   $151.20  
  7 purchase totals = $932.74       $1,013.3001   $1,013.30   $1,013.25   $1,013.40