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	$124.51	8.798%	$135.4644	$135.46	$135.45	$135.50
Purchase #2	$201.50	6.419%	$214.4343	$214.43	$214.45	$214.40
Purchase #3	$229.48	12.479%	$258.1168	$258.12	$258.10	$258.10
Purchase #4	$96.42	9.481%	$105.5616	$105.56	$105.55	$105.60
Purchase #5	$102.61	6.752%	$109.5382	$109.54	$109.55	$109.50
Purchase #6	$182.91	8.438%	$198.3439	$198.34	$198.35	$198.30
Purchase #7	$67.77	6.255%	$72.009	$72.01	$72.00	$72.00
7 purchase totals =	$1,005.20		$1,093.4682	$1,093.46	$1,093.45	$1,093.40