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 $228.64   7.654%   $246.1401   $246.14   $246.15   $246.10  
  Purchase #2 $60.44   4.260%   $63.0147   $63.01   $63.00   $63.00  
  Purchase #3 $33.67   3.129%   $34.7235   $34.72   $34.70   $34.70  
  Purchase #4 $153.73   7.826%   $165.7609   $165.76   $165.75   $165.80  
  Purchase #5 $70.32   5.565%   $74.2333   $74.23   $74.25   $74.20  
  Purchase #6 $143.98   9.227%   $157.265   $157.27   $157.25   $157.30  
  Purchase #7 $193.38   4.180%   $201.4633   $201.46   $201.45   $201.50  
  7 purchase totals = $884.16       $942.6008   $942.59   $942.55   $942.60