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 $187.56   9.372%   $205.1381   $205.14   $205.15   $205.10  
  Purchase #2 $164.88   5.161%   $173.3895   $173.39   $173.40   $173.40  
  Purchase #3 $194.77   12.792%   $219.685   $219.69   $219.70   $219.70  
  Purchase #4 $94.44   13.766%   $107.4406   $107.44   $107.45   $107.40  
  Purchase #5 $149.56   8.151%   $161.7506   $161.75   $161.75   $161.80  
  Purchase #6 $107.43   8.423%   $116.4788   $116.48   $116.50   $116.50  
  Purchase #7 $37.94   12.413%   $42.6495   $42.65   $42.65   $42.60  
  7 purchase totals = $936.58       $1,026.5321   $1,026.54   $1,026.60   $1,026.50