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 $63.32   8.191%   $68.5065   $68.51   $68.50   $68.50  
  Purchase #2 $245.96   10.833%   $272.6048   $272.60   $272.60   $272.60  
  Purchase #3 $109.84   8.609%   $119.2961   $119.30   $119.30   $119.30  
  Purchase #4 $236.74   8.599%   $257.0973   $257.10   $257.10   $257.10  
  Purchase #5 $130.76   10.338%   $144.278   $144.28   $144.30   $144.30  
  Purchase #6 $249.67   8.427%   $270.7097   $270.71   $270.70   $270.70  
  Purchase #7 $236.55   13.111%   $267.5641   $267.56   $267.55   $267.60  
  7 purchase totals = $1,272.84       $1,400.0565   $1,400.06   $1,400.05   $1,400.10