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 $63.59   9.215%   $69.4498   $69.45   $69.45   $69.40  
  Purchase #2 $89.35   10.811%   $99.0096   $99.01   $99.00   $99.00  
  Purchase #3 $71.55   3.867%   $74.3168   $74.32   $74.30   $74.30  
  Purchase #4 $212.91   13.656%   $241.985   $241.99   $242.00   $242.00  
  Purchase #5 $191.99   6.817%   $205.078   $205.08   $205.10   $205.10  
  Purchase #6 $51.33   12.351%   $57.6698   $57.67   $57.65   $57.70  
  Purchase #7 $42.46   11.807%   $47.4733   $47.47   $47.45   $47.50  
  7 purchase totals = $723.18       $794.9823   $794.99   $794.95   $795.00