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	$134.41	11.829%	$150.3094	$150.31	$150.30	$150.30
Purchase #2	$12.81	9.713%	$14.0542	$14.05	$14.05	$14.10
Purchase #3	$59.73	3.297%	$61.6993	$61.70	$61.70	$61.70
Purchase #4	$96.31	4.185%	$100.3406	$100.34	$100.35	$100.30
Purchase #5	$158.60	7.648%	$170.7297	$170.73	$170.75	$170.70
Purchase #6	$86.36	11.635%	$96.408	$96.41	$96.40	$96.40
Purchase #7	$65.66	11.234%	$73.0362	$73.04	$73.05	$73.00
7 purchase totals =	$613.88		$666.5774	$666.58	$666.60	$666.50