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	$31.91	4.834%	$33.4525	$33.45	$33.45	$33.50
Purchase #2	$168.71	7.814%	$181.893	$181.89	$181.90	$181.90
Purchase #3	$151.66	9.228%	$165.6552	$165.66	$165.65	$165.70
Purchase #4	$10.77	4.118%	$11.2135	$11.21	$11.20	$11.20
Purchase #5	$59.34	12.383%	$66.6881	$66.69	$66.70	$66.70
Purchase #6	$89.85	7.416%	$96.5133	$96.51	$96.50	$96.50
Purchase #7	$240.53	11.582%	$268.3882	$268.39	$268.40	$268.40
7 purchase totals =	$752.77		$823.8038	$823.80	$823.80	$823.90