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 $65.94   10.692%   $72.9903   $72.99   $73.00   $73.00  
  Purchase #2 $11.47   5.780%   $12.133   $12.13   $12.15   $12.10  
  Purchase #3 $65.33   8.611%   $70.9556   $70.96   $70.95   $71.00  
  Purchase #4 $42.94   4.265%   $44.7714   $44.77   $44.75   $44.80  
  Purchase #5 $15.44   11.425%   $17.204   $17.20   $17.20   $17.20  
  Purchase #6 $209.41   10.600%   $231.6075   $231.61   $231.60   $231.60  
  Purchase #7 $63.45   3.701%   $65.7983   $65.80   $65.80   $65.80  
  7 purchase totals = $473.98       $515.4601   $515.46   $515.45   $515.50