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 $61.29   9.741%   $67.2603   $67.26   $67.25   $67.30  
  Purchase #2 $183.42   4.273%   $191.2575   $191.26   $191.25   $191.30  
  Purchase #3 $139.93   13.790%   $159.2263   $159.23   $159.25   $159.20  
  Purchase #4 $117.53   9.461%   $128.6495   $128.65   $128.65   $128.60  
  Purchase #5 $157.44   11.112%   $174.9347   $174.93   $174.95   $174.90  
  Purchase #6 $185.25   3.117%   $191.0242   $191.02   $191.00   $191.00  
  Purchase #7 $127.87   11.363%   $142.3999   $142.40   $142.40   $142.40  
  7 purchase totals = $972.73       $1,054.7524   $1,054.75   $1,054.75   $1,054.70