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 $210.75   5.872%   $223.1252   $223.13   $223.15   $223.10  
  Purchase #2 $193.77   13.439%   $219.8108   $219.81   $219.80   $219.80  
  Purchase #3 $201.34   7.186%   $215.8083   $215.81   $215.80   $215.80  
  Purchase #4 $236.70   13.209%   $267.9657   $267.97   $267.95   $268.00  
  Purchase #5 $112.43   5.454%   $118.5619   $118.56   $118.55   $118.60  
  Purchase #6 $152.29   3.752%   $158.0039   $158.00   $158.00   $158.00  
  Purchase #7 $88.56   6.524%   $94.3377   $94.34   $94.35   $94.30  
  7 purchase totals = $1,195.84       $1,297.6135   $1,297.62   $1,297.60   $1,297.60