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 $89.38   7.520%   $96.1014   $96.10   $96.10   $96.10  
  Purchase #2 $249.84   9.769%   $274.2469   $274.25   $274.25   $274.20  
  Purchase #3 $16.45   4.363%   $17.1677   $17.17   $17.15   $17.20  
  Purchase #4 $101.49   5.787%   $107.3632   $107.36   $107.35   $107.40  
  Purchase #5 $9.87   5.631%   $10.4258   $10.43   $10.45   $10.40  
  Purchase #6 $54.92   6.683%   $58.5903   $58.59   $58.60   $58.60  
  Purchase #7 $128.83   8.282%   $139.4997   $139.50   $139.50   $139.50  
  7 purchase totals = $650.78       $703.3950   $703.40   $703.40   $703.40