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 $49.47   8.762%   $53.8046   $53.80   $53.80   $53.80  
  Purchase #2 $23.85   9.104%   $26.0213   $26.02   $26.00   $26.00  
  Purchase #3 $212.77   11.295%   $236.8024   $236.80   $236.80   $236.80  
  Purchase #4 $32.53   5.514%   $34.3237   $34.32   $34.30   $34.30  
  Purchase #5 $161.36   3.751%   $167.4126   $167.41   $167.40   $167.40  
  Purchase #6 $35.95   11.524%   $40.0929   $40.09   $40.10   $40.10  
  Purchase #7 $250.87   10.384%   $276.9203   $276.92   $276.90   $276.90  
  7 purchase totals = $766.80       $835.3778   $835.36   $835.30   $835.30