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	$215.64	4.435%	$225.2036	$225.20	$225.20	$225.20
Purchase #2	$245.38	12.359%	$275.7065	$275.71	$275.70	$275.70
Purchase #3	$170.56	11.634%	$190.403	$190.40	$190.40	$190.40
Purchase #4	$146.31	12.137%	$164.0676	$164.07	$164.05	$164.10
Purchase #5	$47.58	13.276%	$53.8967	$53.90	$53.90	$53.90
Purchase #6	$229.50	6.201%	$243.7313	$243.73	$243.75	$243.70
Purchase #7	$229.62	3.794%	$238.3318	$238.33	$238.35	$238.30
7 purchase totals =	$1,284.59		$1,391.3405	$1,391.34	$1,391.35	$1,391.30