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	$235.56	3.434%	$243.6491	$243.65	$243.65	$243.60
Purchase #2	$70.72	11.474%	$78.8344	$78.83	$78.85	$78.80
Purchase #3	$220.31	3.172%	$227.2982	$227.30	$227.30	$227.30
Purchase #4	$31.28	13.664%	$35.5541	$35.55	$35.55	$35.60
Purchase #5	$106.55	3.707%	$110.4998	$110.50	$110.50	$110.50
Purchase #6	$28.29	11.109%	$31.4327	$31.43	$31.45	$31.40
Purchase #7	$44.74	5.736%	$47.3063	$47.31	$47.30	$47.30
7 purchase totals =	$737.45		$774.5746	$774.57	$774.60	$774.50