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	$90.86	6.203%	$96.496	$96.50	$96.50	$96.50
Purchase #2	$130.87	7.301%	$140.4248	$140.42	$140.40	$140.40
Purchase #3	$119.31	9.230%	$130.3223	$130.32	$130.30	$130.30
Purchase #4	$143.49	4.654%	$150.168	$150.17	$150.15	$150.20
Purchase #5	$90.89	8.430%	$98.552	$98.55	$98.55	$98.60
Purchase #6	$20.42	4.798%	$21.3998	$21.40	$21.40	$21.40
Purchase #7	$246.31	7.222%	$264.0985	$264.10	$264.10	$264.10
7 purchase totals =	$842.15		$901.4614	$901.46	$901.40	$901.50