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 $62.60   6.538%   $66.6928   $66.69   $66.70   $66.70  
  Purchase #2 $144.84   11.125%   $160.9535   $160.95   $160.95   $161.00  
  Purchase #3 $193.66   12.786%   $218.4214   $218.42   $218.40   $218.40  
  Purchase #4 $125.62   11.395%   $139.9344   $139.93   $139.95   $139.90  
  Purchase #5 $138.73   3.192%   $143.1583   $143.16   $143.15   $143.20  
  Purchase #6 $126.93   12.660%   $142.9993   $143.00   $143.00   $143.00  
  Purchase #7 $166.99   11.597%   $186.3558   $186.36   $186.35   $186.40  
  7 purchase totals = $959.37       $1,058.5155   $1,058.51   $1,058.50   $1,058.60