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	$122.88	6.173%	$130.4654	$130.47	$130.45	$130.50
Purchase #2	$219.56	13.713%	$249.6683	$249.67	$249.65	$249.70
Purchase #3	$49.31	5.290%	$51.9185	$51.92	$51.90	$51.90
Purchase #4	$30.73	4.864%	$32.2247	$32.22	$32.20	$32.20
Purchase #5	$238.45	11.369%	$265.5594	$265.56	$265.55	$265.60
Purchase #6	$123.41	6.712%	$131.6933	$131.69	$131.70	$131.70
Purchase #7	$236.91	5.758%	$250.5513	$250.55	$250.55	$250.60
7 purchase totals =	$1,021.25		$1,112.0809	$1,112.08	$1,112.00	$1,112.20