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	$91.85	9.404%	$100.4876	$100.49	$100.50	$100.50
Purchase #2	$175.52	4.185%	$182.8655	$182.87	$182.85	$182.90
Purchase #3	$67.88	13.480%	$77.0302	$77.03	$77.05	$77.00
Purchase #4	$55.69	7.716%	$59.987	$59.99	$60.00	$60.00
Purchase #5	$130.53	13.623%	$148.3121	$148.31	$148.30	$148.30
Purchase #6	$250.31	4.537%	$261.6666	$261.67	$261.65	$261.70
Purchase #7	$86.73	3.651%	$89.8965	$89.90	$89.90	$89.90
7 purchase totals =	$858.51		$920.2455	$920.26	$920.25	$920.30