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	$78.49	12.437%	$88.2518	$88.25	$88.25	$88.30
Purchase #2	$7.82	6.152%	$8.3011	$8.30	$8.30	$8.30
Purchase #3	$175.56	6.391%	$186.78	$186.78	$186.80	$186.80
Purchase #4	$84.68	7.111%	$90.7016	$90.70	$90.70	$90.70
Purchase #5	$83.81	11.686%	$93.604	$93.60	$93.60	$93.60
Purchase #6	$41.45	9.589%	$45.4246	$45.42	$45.40	$45.40
Purchase #7	$83.47	6.483%	$88.8814	$88.88	$88.90	$88.90
7 purchase totals =	$555.28		$601.9445	$601.93	$601.95	$602.00