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 $59.37   6.578%   $63.2754   $63.28   $63.30   $63.30  
  Purchase #2 $134.71   3.555%   $139.4989   $139.50   $139.50   $139.50  
  Purchase #3 $24.66   5.348%   $25.9788   $25.98   $26.00   $26.00  
  Purchase #4 $219.32   6.134%   $232.7731   $232.77   $232.75   $232.80  
  Purchase #5 $224.56   9.729%   $246.4074   $246.41   $246.40   $246.40  
  Purchase #6 $191.42   5.871%   $202.6583   $202.66   $202.65   $202.70  
  Purchase #7 $23.30   3.106%   $24.0237   $24.02   $24.00   $24.00  
  7 purchase totals = $877.34       $934.6156   $934.62   $934.60   $934.70