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 $60.95   9.825%   $66.9383   $66.94   $66.95   $66.90  
  Purchase #2 $61.99   7.546%   $66.6678   $66.67   $66.65   $66.70  
  Purchase #3 $77.49   13.511%   $87.9597   $87.96   $87.95   $88.00  
  Purchase #4 $62.58   13.110%   $70.7842   $70.78   $70.80   $70.80  
  Purchase #5 $111.63   12.507%   $125.5916   $125.59   $125.60   $125.60  
  Purchase #6 $249.93   13.160%   $282.8208   $282.82   $282.80   $282.80  
  Purchase #7 $177.95   10.274%   $196.2326   $196.23   $196.25   $196.20  
  7 purchase totals = $802.52       $896.9950   $896.99   $897.00   $897.00