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 $60.57   6.196%   $64.3229   $64.32   $64.30   $64.30  
  Purchase #2 $186.91   11.309%   $208.0477   $208.05   $208.05   $208.00  
  Purchase #3 $13.71   7.169%   $14.6929   $14.69   $14.70   $14.70  
  Purchase #4 $137.59   3.544%   $142.4662   $142.47   $142.45   $142.50  
  Purchase #5 $189.94   11.578%   $211.9313   $211.93   $211.95   $211.90  
  Purchase #6 $167.37   13.766%   $190.4102   $190.41   $190.40   $190.40  
  Purchase #7 $206.49   10.860%   $228.9148   $228.91   $228.90   $228.90  
  7 purchase totals = $962.58       $1,060.7860   $1,060.78   $1,060.75   $1,060.70