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 $91.41   10.626%   $101.1232   $101.12   $101.10   $101.10  
  Purchase #2 $78.51   11.535%   $87.5661   $87.57   $87.55   $87.60  
  Purchase #3 $104.53   13.582%   $118.7273   $118.73   $118.75   $118.70  
  Purchase #4 $237.43   12.663%   $267.4958   $267.50   $267.50   $267.50  
  Purchase #5 $234.81   4.453%   $245.2661   $245.27   $245.25   $245.30  
  Purchase #6 $160.49   3.394%   $165.937   $165.94   $165.95   $165.90  
  Purchase #7 $67.87   13.301%   $76.8974   $76.90   $76.90   $76.90  
  7 purchase totals = $975.05       $1,063.0129   $1,063.03   $1,063.00   $1,063.00