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	$73.89	9.376%	$80.8179	$80.82	$80.80	$80.80
Purchase #2	$34.94	6.700%	$37.281	$37.28	$37.30	$37.30
Purchase #3	$86.33	8.357%	$93.5446	$93.54	$93.55	$93.50
Purchase #4	$61.50	5.476%	$64.8677	$64.87	$64.85	$64.90
Purchase #5	$7.60	4.322%	$7.9285	$7.93	$7.95	$7.90
Purchase #6	$229.91	12.696%	$259.0994	$259.10	$259.10	$259.10
Purchase #7	$148.34	3.773%	$153.9369	$153.94	$153.95	$153.90
7 purchase totals =	$642.51		$697.4760	$697.48	$697.50	$697.40