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	$46.45	8.832%	$50.5525	$50.55	$50.55	$50.60
Purchase #2	$223.36	9.369%	$244.2866	$244.29	$244.30	$244.30
Purchase #3	$98.78	7.808%	$106.4927	$106.49	$106.50	$106.50
Purchase #4	$243.41	4.134%	$253.4726	$253.47	$253.45	$253.50
Purchase #5	$86.37	10.471%	$95.4138	$95.41	$95.40	$95.40
Purchase #6	$40.41	4.751%	$42.3299	$42.33	$42.35	$42.30
Purchase #7	$248.95	10.396%	$274.8308	$274.83	$274.85	$274.80
7 purchase totals =	$987.73		$1,067.3789	$1,067.37	$1,067.40	$1,067.40