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 $232.86   6.651%   $248.3475   $248.35   $248.35   $248.30  
  Purchase #2 $150.87   5.473%   $159.1271   $159.13   $159.15   $159.10  
  Purchase #3 $245.48   8.504%   $266.3556   $266.36   $266.35   $266.40  
  Purchase #4 $170.72   12.412%   $191.9098   $191.91   $191.90   $191.90  
  Purchase #5 $186.61   10.368%   $205.9577   $205.96   $205.95   $206.00  
  Purchase #6 $115.75   9.735%   $127.0183   $127.02   $127.00   $127.00  
  Purchase #7 $209.35   3.764%   $217.2299   $217.23   $217.25   $217.20  
  7 purchase totals = $1,311.64       $1,415.9459   $1,415.96   $1,415.95   $1,415.90