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 $14.60   7.783%   $15.7363   $15.74   $15.75   $15.70  
  Purchase #2 $150.79   8.131%   $163.0507   $163.05   $163.05   $163.10  
  Purchase #3 $153.57   8.608%   $166.7893   $166.79   $166.80   $166.80  
  Purchase #4 $160.59   7.280%   $172.281   $172.28   $172.30   $172.30  
  Purchase #5 $40.48   13.730%   $46.0379   $46.04   $46.05   $46.00  
  Purchase #6 $108.77   3.725%   $112.8217   $112.82   $112.80   $112.80  
  Purchase #7 $10.80   3.458%   $11.1735   $11.17   $11.15   $11.20  
  7 purchase totals = $639.60       $687.8904   $687.89   $687.90   $687.90