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 $57.57   8.138%   $62.255   $62.26   $62.25   $62.30  
  Purchase #2 $40.68   8.548%   $44.1573   $44.16   $44.15   $44.20  
  Purchase #3 $215.78   7.370%   $231.683   $231.68   $231.70   $231.70  
  Purchase #4 $247.57   11.633%   $276.3698   $276.37   $276.35   $276.40  
  Purchase #5 $134.36   8.212%   $145.3936   $145.39   $145.40   $145.40  
  Purchase #6 $98.38   11.812%   $110.0006   $110.00   $110.00   $110.00  
  Purchase #7 $37.71   9.236%   $41.1929   $41.19   $41.20   $41.20  
  7 purchase totals = $832.05       $911.0522   $911.05   $911.05   $911.20