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 $96.85   11.578%   $108.0633   $108.06   $108.05   $108.10  
  Purchase #2 $54.64   9.272%   $59.7062   $59.71   $59.70   $59.70  
  Purchase #3 $191.82   8.555%   $208.2302   $208.23   $208.25   $208.20  
  Purchase #4 $49.96   6.378%   $53.1464   $53.15   $53.15   $53.10  
  Purchase #5 $115.58   9.767%   $126.8687   $126.87   $126.85   $126.90  
  Purchase #6 $245.90   8.143%   $265.9236   $265.92   $265.90   $265.90  
  Purchase #7 $39.69   8.339%   $42.9997   $43.00   $43.00   $43.00  
  7 purchase totals = $794.44       $864.9381   $864.94   $864.90   $864.90