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	$87.41	4.368%	$91.2281	$91.23	$91.25	$91.20
Purchase #2	$33.73	9.194%	$36.8311	$36.83	$36.85	$36.80
Purchase #3	$17.98	4.693%	$18.8238	$18.82	$18.80	$18.80
Purchase #4	$91.70	4.591%	$95.9099	$95.91	$95.90	$95.90
Purchase #5	$240.52	10.156%	$264.9472	$264.95	$264.95	$264.90
Purchase #6	$66.66	7.274%	$71.5088	$71.51	$71.50	$71.50
Purchase #7	$72.29	8.138%	$78.173	$78.17	$78.15	$78.20
7 purchase totals =	$610.29		$657.4219	$657.42	$657.40	$657.30