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	$48.96	6.400%	$52.0934	$52.09	$52.10	$52.10
Purchase #2	$188.98	10.670%	$209.1442	$209.14	$209.15	$209.10
Purchase #3	$18.44	12.216%	$20.6926	$20.69	$20.70	$20.70
Purchase #4	$247.52	6.550%	$263.7326	$263.73	$263.75	$263.70
Purchase #5	$91.34	4.481%	$95.4329	$95.43	$95.45	$95.40
Purchase #6	$53.80	13.804%	$61.2266	$61.23	$61.25	$61.20
Purchase #7	$147.85	13.232%	$167.4135	$167.41	$167.40	$167.40
7 purchase totals =	$796.89		$869.7358	$869.72	$869.80	$869.60