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 $196.79   9.685%   $215.8491   $215.85   $215.85   $215.80  
  Purchase #2 $89.57   5.623%   $94.6065   $94.61   $94.60   $94.60  
  Purchase #3 $37.70   11.102%   $41.8855   $41.89   $41.90   $41.90  
  Purchase #4 $212.68   7.431%   $228.4843   $228.48   $228.50   $228.50  
  Purchase #5 $73.44   5.378%   $77.3896   $77.39   $77.40   $77.40  
  Purchase #6 $229.88   4.381%   $239.951   $239.95   $239.95   $240.00  
  Purchase #7 $143.55   7.161%   $153.8296   $153.83   $153.85   $153.80  
  7 purchase totals = $983.61       $1,051.9956   $1,052.00   $1,052.05   $1,052.00