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	$114.55	7.321%	$122.9362	$122.94	$122.95	$122.90
Purchase #2	$75.61	12.712%	$85.2215	$85.22	$85.20	$85.20
Purchase #3	$45.41	10.862%	$50.3424	$50.34	$50.35	$50.30
Purchase #4	$99.85	12.440%	$112.2713	$112.27	$112.25	$112.30
Purchase #5	$157.46	13.775%	$179.1501	$179.15	$179.15	$179.20
Purchase #6	$239.90	4.308%	$250.2349	$250.23	$250.25	$250.20
Purchase #7	$147.89	13.713%	$168.1702	$168.17	$168.15	$168.20
7 purchase totals =	$880.67		$968.3266	$968.32	$968.30	$968.30