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	$218.40	12.123%	$244.8766	$244.88	$244.90	$244.90
Purchase #2	$31.76	11.201%	$35.3174	$35.32	$35.30	$35.30
Purchase #3	$104.67	6.163%	$111.1208	$111.12	$111.10	$111.10
Purchase #4	$43.67	8.782%	$47.5051	$47.51	$47.50	$47.50
Purchase #5	$68.56	5.559%	$72.3713	$72.37	$72.35	$72.40
Purchase #6	$28.31	3.813%	$29.3895	$29.39	$29.40	$29.40
Purchase #7	$247.34	6.378%	$263.1153	$263.12	$263.10	$263.10
7 purchase totals =	$742.71		$803.6960	$803.71	$803.65	$803.70