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 $213.29   11.351%   $237.5005   $237.50   $237.50   $237.50  
  Purchase #2 $114.70   13.317%   $129.9746   $129.97   $129.95   $130.00  
  Purchase #3 $245.30   12.776%   $276.6395   $276.64   $276.65   $276.60  
  Purchase #4 $180.30   11.661%   $201.3248   $201.32   $201.30   $201.30  
  Purchase #5 $164.81   9.562%   $180.5691   $180.57   $180.55   $180.60  
  Purchase #6 $198.37   8.272%   $214.7792   $214.78   $214.80   $214.80  
  Purchase #7 $15.53   12.154%   $17.4175   $17.42   $17.40   $17.40  
  7 purchase totals = $1,132.30       $1,258.2052   $1,258.20   $1,258.15   $1,258.20