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 $117.47   8.705%   $127.6958   $127.70   $127.70   $127.70  
  Purchase #2 $92.53   7.288%   $99.2736   $99.27   $99.25   $99.30  
  Purchase #3 $194.88   3.590%   $201.8762   $201.88   $201.90   $201.90  
  Purchase #4 $156.92   5.868%   $166.1281   $166.13   $166.15   $166.10  
  Purchase #5 $44.98   13.514%   $51.0586   $51.06   $51.05   $51.10  
  Purchase #6 $246.67   11.269%   $274.4672   $274.47   $274.45   $274.50  
  Purchase #7 $130.89   12.643%   $147.4384   $147.44   $147.45   $147.40  
  7 purchase totals = $984.34       $1,067.9379   $1,067.95   $1,067.95   $1,068.00