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	$165.43	13.279%	$187.3974	$187.40	$187.40	$187.40
Purchase #2	$77.34	10.127%	$85.1722	$85.17	$85.15	$85.20
Purchase #3	$54.60	4.653%	$57.1405	$57.14	$57.15	$57.10
Purchase #4	$211.67	7.519%	$227.5855	$227.59	$227.60	$227.60
Purchase #5	$64.85	10.345%	$71.5587	$71.56	$71.55	$71.60
Purchase #6	$43.92	6.653%	$46.842	$46.84	$46.85	$46.80
Purchase #7	$131.38	10.437%	$145.0921	$145.09	$145.10	$145.10
7 purchase totals =	$749.19		$820.7884	$820.79	$820.80	$820.80