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 $26.86   6.292%   $28.55   $28.55   $28.55   $28.60  
  Purchase #2 $225.45   13.216%   $255.2455   $255.25   $255.25   $255.20  
  Purchase #3 $211.57   10.229%   $233.2115   $233.21   $233.20   $233.20  
  Purchase #4 $155.56   3.437%   $160.9066   $160.91   $160.90   $160.90  
  Purchase #5 $126.99   5.396%   $133.8424   $133.84   $133.85   $133.80  
  Purchase #6 $84.90   8.829%   $92.3958   $92.40   $92.40   $92.40  
  Purchase #7 $230.61   13.795%   $262.4226   $262.42   $262.40   $262.40  
  7 purchase totals = $1,061.94       $1,166.5744   $1,166.58   $1,166.55   $1,166.50