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	$124.49	3.873%	$129.3115	$129.31	$129.30	$129.30
Purchase #2	$171.72	6.290%	$182.5212	$182.52	$182.50	$182.50
Purchase #3	$124.88	6.796%	$133.3668	$133.37	$133.35	$133.40
Purchase #4	$61.98	7.804%	$66.8169	$66.82	$66.80	$66.80
Purchase #5	$202.91	6.839%	$216.787	$216.79	$216.80	$216.80
Purchase #6	$86.71	4.275%	$90.4169	$90.42	$90.40	$90.40
Purchase #7	$68.32	3.766%	$70.8929	$70.89	$70.90	$70.90
7 purchase totals =	$841.01		$890.1132	$890.12	$890.05	$890.10