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	$78.66	13.434%	$89.2272	$89.23	$89.25	$89.20
Purchase #2	$59.71	7.325%	$64.0838	$64.08	$64.10	$64.10
Purchase #3	$174.46	3.507%	$180.5783	$180.58	$180.60	$180.60
Purchase #4	$176.63	3.224%	$182.3246	$182.32	$182.30	$182.30
Purchase #5	$159.65	12.595%	$179.7579	$179.76	$179.75	$179.80
Purchase #6	$246.72	5.501%	$260.2921	$260.29	$260.30	$260.30
Purchase #7	$245.29	10.586%	$271.2564	$271.26	$271.25	$271.30
7 purchase totals =	$1,141.12		$1,227.5203	$1,227.52	$1,227.55	$1,227.60