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	$40.56	9.508%	$44.4164	$44.42	$44.40	$44.40
Purchase #2	$186.47	7.501%	$200.4571	$200.46	$200.45	$200.50
Purchase #3	$175.76	5.195%	$184.8907	$184.89	$184.90	$184.90
Purchase #4	$105.99	9.318%	$115.8661	$115.87	$115.85	$115.90
Purchase #5	$76.47	12.386%	$85.9416	$85.94	$85.95	$85.90
Purchase #6	$83.91	6.711%	$89.5412	$89.54	$89.55	$89.50
Purchase #7	$110.51	11.217%	$122.9059	$122.91	$122.90	$122.90
7 purchase totals =	$779.67		$844.0190	$844.03	$844.00	$844.00