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	$30.28	11.353%	$33.7177	$33.72	$33.70	$33.70
Purchase #2	$128.61	10.670%	$142.3327	$142.33	$142.35	$142.30
Purchase #3	$147.63	13.481%	$167.532	$167.53	$167.55	$167.50
Purchase #4	$5.56	4.195%	$5.7932	$5.79	$5.80	$5.80
Purchase #5	$186.84	5.165%	$196.4903	$196.49	$196.50	$196.50
Purchase #6	$53.68	5.873%	$56.8326	$56.83	$56.85	$56.80
Purchase #7	$190.56	9.294%	$208.2706	$208.27	$208.25	$208.30
7 purchase totals =	$743.16		$810.9691	$810.96	$811.00	$810.90