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 $34.64   11.495%   $38.6219   $38.62   $38.60   $38.60  
  Purchase #2 $68.75   3.501%   $71.1569   $71.16   $71.15   $71.20  
  Purchase #3 $182.71   3.175%   $188.511   $188.51   $188.50   $188.50  
  Purchase #4 $47.63   11.121%   $52.9269   $52.93   $52.95   $52.90  
  Purchase #5 $84.83   3.113%   $87.4708   $87.47   $87.45   $87.50  
  Purchase #6 $245.63   7.768%   $264.7105   $264.71   $264.70   $264.70  
  Purchase #7 $88.36   5.582%   $93.2923   $93.29   $93.30   $93.30  
  7 purchase totals = $752.55       $796.6903   $796.69   $796.65   $796.70