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	$221.46	4.474%	$231.3681	$231.37	$231.35	$231.40
Purchase #2	$110.92	11.133%	$123.2687	$123.27	$123.25	$123.30
Purchase #3	$181.31	12.835%	$204.5811	$204.58	$204.60	$204.60
Purchase #4	$109.89	12.701%	$123.8471	$123.85	$123.85	$123.80
Purchase #5	$65.25	9.138%	$71.2125	$71.21	$71.20	$71.20
Purchase #6	$155.48	11.382%	$173.1767	$173.18	$173.20	$173.20
Purchase #7	$61.47	12.445%	$69.1199	$69.12	$69.10	$69.10
7 purchase totals =	$905.78		$996.5741	$996.58	$996.55	$996.60