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	$244.92	13.715%	$278.5108	$278.51	$278.50	$278.50
Purchase #2	$80.96	9.146%	$88.3646	$88.36	$88.35	$88.40
Purchase #3	$175.99	3.729%	$182.5527	$182.55	$182.55	$182.60
Purchase #4	$39.93	6.118%	$42.3729	$42.37	$42.35	$42.40
Purchase #5	$74.84	13.460%	$84.9135	$84.91	$84.90	$84.90
Purchase #6	$127.56	13.580%	$144.8826	$144.88	$144.90	$144.90
Purchase #7	$67.76	7.488%	$72.8339	$72.83	$72.85	$72.80
7 purchase totals =	$811.96		$894.4310	$894.41	$894.40	$894.50