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	$234.72	6.155%	$249.167	$249.17	$249.15	$249.20
Purchase #2	$97.75	11.840%	$109.3236	$109.32	$109.30	$109.30
Purchase #3	$74.73	11.315%	$83.1857	$83.19	$83.20	$83.20
Purchase #4	$132.32	11.134%	$147.0525	$147.05	$147.05	$147.10
Purchase #5	$146.45	4.651%	$153.2614	$153.26	$153.25	$153.30
Purchase #6	$234.52	3.821%	$243.481	$243.48	$243.50	$243.50
Purchase #7	$29.51	12.574%	$33.2206	$33.22	$33.20	$33.20
7 purchase totals =	$950.00		$1,018.6918	$1,018.69	$1,018.65	$1,018.80