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	$199.87	10.479%	$220.8144	$220.81	$220.80	$220.80
Purchase #2	$50.63	12.384%	$56.9	$56.90	$56.90	$56.90
Purchase #3	$250.31	5.680%	$264.5276	$264.53	$264.55	$264.50
Purchase #4	$100.62	12.180%	$112.8755	$112.88	$112.90	$112.90
Purchase #5	$183.54	4.544%	$191.8801	$191.88	$191.90	$191.90
Purchase #6	$223.38	4.637%	$233.7381	$233.74	$233.75	$233.70
Purchase #7	$73.25	5.224%	$77.0766	$77.08	$77.10	$77.10
7 purchase totals =	$1,081.60		$1,157.8123	$1,157.82	$1,157.90	$1,157.80