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 $54.84   10.532%   $60.6157   $60.62   $60.60   $60.60  
  Purchase #2 $250.89   5.292%   $264.1671   $264.17   $264.15   $264.20  
  Purchase #3 $22.44   9.627%   $24.6003   $24.60   $24.60   $24.60  
  Purchase #4 $87.69   3.839%   $91.0564   $91.06   $91.05   $91.10  
  Purchase #5 $77.42   5.290%   $81.5155   $81.52   $81.50   $81.50  
  Purchase #6 $136.41   13.563%   $154.9113   $154.91   $154.90   $154.90  
  Purchase #7 $87.50   10.649%   $96.8179   $96.82   $96.80   $96.80  
  7 purchase totals = $717.19       $773.6842   $773.70   $773.60   $773.70