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 $221.38   11.402%   $246.6217   $246.62   $246.60   $246.60  
  Purchase #2 $158.85   4.448%   $165.9156   $165.92   $165.90   $165.90  
  Purchase #3 $177.43   8.868%   $193.1645   $193.16   $193.15   $193.20  
  Purchase #4 $51.62   12.388%   $58.0147   $58.01   $58.00   $58.00  
  Purchase #5 $246.42   9.693%   $270.3055   $270.31   $270.30   $270.30  
  Purchase #6 $76.67   8.867%   $83.4683   $83.47   $83.45   $83.50  
  Purchase #7 $93.93   10.186%   $103.4977   $103.50   $103.50   $103.50  
  7 purchase totals = $1,026.30       $1,120.9880   $1,120.99   $1,120.90   $1,121.00