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	$39.84	7.631%	$42.8802	$42.88	$42.90	$42.90
Purchase #2	$164.62	9.533%	$180.3132	$180.31	$180.30	$180.30
Purchase #3	$33.27	7.869%	$35.888	$35.89	$35.90	$35.90
Purchase #4	$113.44	9.831%	$124.5923	$124.59	$124.60	$124.60
Purchase #5	$236.83	5.266%	$249.3015	$249.30	$249.30	$249.30
Purchase #6	$104.78	7.756%	$112.9067	$112.91	$112.90	$112.90
Purchase #7	$231.86	11.657%	$258.8879	$258.89	$258.90	$258.90
7 purchase totals =	$924.64		$1,004.7698	$1,004.77	$1,004.80	$1,004.80