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	$165.72	13.533%	$188.1469	$188.15	$188.15	$188.10
Purchase #2	$73.76	6.799%	$78.7749	$78.77	$78.75	$78.80
Purchase #3	$134.98	8.730%	$146.7638	$146.76	$146.75	$146.80
Purchase #4	$249.80	7.199%	$267.7831	$267.78	$267.80	$267.80
Purchase #5	$190.52	4.524%	$199.1391	$199.14	$199.15	$199.10
Purchase #6	$71.92	12.487%	$80.9007	$80.90	$80.90	$80.90
Purchase #7	$239.86	4.137%	$249.783	$249.78	$249.80	$249.80
7 purchase totals =	$1,126.56		$1,211.2915	$1,211.28	$1,211.30	$1,211.30