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	$123.63	13.656%	$140.5129	$140.51	$140.50	$140.50
Purchase #2	$80.40	3.805%	$83.4592	$83.46	$83.45	$83.50
Purchase #3	$159.82	9.656%	$175.2522	$175.25	$175.25	$175.30
Purchase #4	$100.41	3.338%	$103.7617	$103.76	$103.75	$103.80
Purchase #5	$205.51	8.654%	$223.2948	$223.29	$223.30	$223.30
Purchase #6	$11.35	10.526%	$12.5447	$12.54	$12.55	$12.50
Purchase #7	$152.97	9.369%	$167.3018	$167.30	$167.30	$167.30
7 purchase totals =	$834.09		$906.1273	$906.11	$906.10	$906.20