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	$241.54	13.215%	$273.4595	$273.46	$273.45	$273.50
Purchase #2	$134.48	8.557%	$145.9875	$145.99	$146.00	$146.00
Purchase #3	$86.56	3.659%	$89.7272	$89.73	$89.75	$89.70
Purchase #4	$125.55	6.115%	$133.2274	$133.23	$133.25	$133.20
Purchase #5	$51.46	5.827%	$54.4586	$54.46	$54.45	$54.50
Purchase #6	$92.92	3.799%	$96.45	$96.45	$96.45	$96.50
Purchase #7	$36.52	3.225%	$37.6978	$37.70	$37.70	$37.70
7 purchase totals =	$769.03		$831.0080	$831.02	$831.05	$831.10