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	$77.73	3.595%	$80.5244	$80.52	$80.50	$80.50
Purchase #2	$118.88	13.284%	$134.672	$134.67	$134.65	$134.70
Purchase #3	$62.88	7.736%	$67.7444	$67.74	$67.75	$67.70
Purchase #4	$117.89	10.545%	$130.3215	$130.32	$130.30	$130.30
Purchase #5	$244.28	6.180%	$259.3765	$259.38	$259.40	$259.40
Purchase #6	$154.89	8.454%	$167.9844	$167.98	$168.00	$168.00
Purchase #7	$85.72	7.282%	$91.9621	$91.96	$91.95	$92.00
7 purchase totals =	$862.27		$932.5853	$932.57	$932.55	$932.60