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	$35.97	4.369%	$37.5415	$37.54	$37.55	$37.50
Purchase #2	$55.86	10.628%	$61.7968	$61.80	$61.80	$61.80
Purchase #3	$85.41	6.568%	$91.0197	$91.02	$91.00	$91.00
Purchase #4	$46.47	5.111%	$48.8451	$48.85	$48.85	$48.80
Purchase #5	$66.73	4.392%	$69.6608	$69.66	$69.65	$69.70
Purchase #6	$28.38	12.284%	$31.8662	$31.87	$31.85	$31.90
Purchase #7	$155.47	4.633%	$162.6729	$162.67	$162.65	$162.70
7 purchase totals =	$474.29		$503.4030	$503.41	$503.35	$503.40