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 $88.54   6.226%   $94.0525   $94.05   $94.05   $94.10  
  Purchase #2 $204.83   13.265%   $232.0007   $232.00   $232.00   $232.00  
  Purchase #3 $30.63   13.609%   $34.7984   $34.80   $34.80   $34.80  
  Purchase #4 $108.75   5.588%   $114.827   $114.83   $114.85   $114.80  
  Purchase #5 $242.38   3.698%   $251.3432   $251.34   $251.35   $251.30  
  Purchase #6 $71.95   5.665%   $76.026   $76.03   $76.05   $76.00  
  Purchase #7 $37.87   12.553%   $42.6238   $42.62   $42.60   $42.60  
  7 purchase totals = $784.95       $845.6716   $845.67   $845.70   $845.60