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 $131.93   10.380%   $145.6243   $145.62   $145.60   $145.60  
  Purchase #2 $76.62   11.388%   $85.3455   $85.35   $85.35   $85.30  
  Purchase #3 $30.41   8.834%   $33.0964   $33.10   $33.10   $33.10  
  Purchase #4 $157.89   10.287%   $174.1321   $174.13   $174.15   $174.10  
  Purchase #5 $68.97   5.243%   $72.5861   $72.59   $72.60   $72.60  
  Purchase #6 $160.96   9.686%   $176.5506   $176.55   $176.55   $176.60  
  Purchase #7 $205.60   7.179%   $220.36   $220.36   $220.35   $220.40  
  7 purchase totals = $832.38       $907.6950   $907.70   $907.70   $907.70