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 $157.87   11.398%   $175.864   $175.86   $175.85   $175.90  
  Purchase #2 $9.28   7.720%   $9.9964   $10.00   $10.00   $10.00  
  Purchase #3 $151.38   9.509%   $165.7747   $165.77   $165.75   $165.80  
  Purchase #4 $225.88   6.849%   $241.3505   $241.35   $241.35   $241.40  
  Purchase #5 $175.51   5.844%   $185.7668   $185.77   $185.75   $185.80  
  Purchase #6 $98.54   10.470%   $108.8571   $108.86   $108.85   $108.90  
  Purchase #7 $13.63   5.249%   $14.3454   $14.35   $14.35   $14.30  
  7 purchase totals = $832.09       $901.9549   $901.96   $901.90   $902.10