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	$175.77	9.112%	$191.7862	$191.79	$191.80	$191.80
Purchase #2	$39.45	7.859%	$42.5504	$42.55	$42.55	$42.60
Purchase #3	$145.83	11.656%	$162.8279	$162.83	$162.85	$162.80
Purchase #4	$184.70	3.208%	$190.6252	$190.63	$190.65	$190.60
Purchase #5	$45.87	9.618%	$50.2818	$50.28	$50.30	$50.30
Purchase #6	$244.82	10.404%	$270.2911	$270.29	$270.30	$270.30
Purchase #7	$238.97	3.567%	$247.4941	$247.49	$247.50	$247.50
7 purchase totals =	$1,075.41		$1,155.8567	$1,155.86	$1,155.95	$1,155.90