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 $64.70   5.767%   $68.4312   $68.43   $68.45   $68.40  
  Purchase #2 $144.75   5.704%   $153.0065   $153.01   $153.00   $153.00  
  Purchase #3 $243.34   5.797%   $257.4464   $257.45   $257.45   $257.40  
  Purchase #4 $250.46   12.375%   $281.4544   $281.45   $281.45   $281.50  
  Purchase #5 $244.41   13.811%   $278.1655   $278.17   $278.15   $278.20  
  Purchase #6 $114.98   11.532%   $128.2395   $128.24   $128.25   $128.20  
  Purchase #7 $206.28   12.169%   $231.3822   $231.38   $231.40   $231.40  
  7 purchase totals = $1,268.92       $1,398.1257   $1,398.13   $1,398.15   $1,398.10