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 $92.64   12.155%   $103.9004   $103.90   $103.90   $103.90  
  Purchase #2 $62.68   12.163%   $70.3038   $70.30   $70.30   $70.30  
  Purchase #3 $41.71   13.473%   $47.3296   $47.33   $47.35   $47.30  
  Purchase #4 $196.94   8.138%   $212.967   $212.97   $212.95   $213.00  
  Purchase #5 $78.32   13.335%   $88.764   $88.76   $88.75   $88.80  
  Purchase #6 $188.68   11.109%   $209.6405   $209.64   $209.65   $209.60  
  Purchase #7 $250.81   6.739%   $267.7121   $267.71   $267.70   $267.70  
  7 purchase totals = $911.78       $1,000.6174   $1,000.61   $1,000.60   $1,000.60