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	$48.52	12.362%	$54.518	$54.52	$54.50	$54.50
Purchase #2	$235.74	5.438%	$248.5595	$248.56	$248.55	$248.60
Purchase #3	$85.29	5.759%	$90.2019	$90.20	$90.20	$90.20
Purchase #4	$90.80	13.218%	$102.8019	$102.80	$102.80	$102.80
Purchase #5	$229.61	9.360%	$251.1015	$251.10	$251.10	$251.10
Purchase #6	$155.76	7.766%	$167.8563	$167.86	$167.85	$167.90
Purchase #7	$212.31	13.295%	$240.5366	$240.54	$240.55	$240.50
7 purchase totals =	$1,058.03		$1,155.5757	$1,155.58	$1,155.55	$1,155.60