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	$134.87	4.447%	$140.8677	$140.87	$140.85	$140.90
Purchase #2	$128.61	7.211%	$137.8841	$137.88	$137.90	$137.90
Purchase #3	$161.91	10.185%	$178.4005	$178.40	$178.40	$178.40
Purchase #4	$79.87	6.574%	$85.1207	$85.12	$85.10	$85.10
Purchase #5	$30.35	7.609%	$32.6593	$32.66	$32.65	$32.70
Purchase #6	$37.33	12.839%	$42.1228	$42.12	$42.10	$42.10
Purchase #7	$184.86	12.746%	$208.4223	$208.42	$208.40	$208.40
7 purchase totals =	$757.80		$825.4774	$825.47	$825.40	$825.50