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	$181.81	4.132%	$189.3224	$189.32	$189.30	$189.30
Purchase #2	$149.53	4.144%	$155.7265	$155.73	$155.75	$155.70
Purchase #3	$154.37	9.618%	$169.2173	$169.22	$169.20	$169.20
Purchase #4	$172.91	6.674%	$184.45	$184.45	$184.45	$184.50
Purchase #5	$137.59	7.404%	$147.7772	$147.78	$147.80	$147.80
Purchase #6	$33.26	11.600%	$37.1182	$37.12	$37.10	$37.10
Purchase #7	$54.80	7.384%	$58.8464	$58.85	$58.85	$58.80
7 purchase totals =	$884.27		$942.4580	$942.47	$942.45	$942.40