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	$72.86	13.385%	$82.6123	$82.61	$82.60	$82.60
Purchase #2	$227.31	9.663%	$249.275	$249.28	$249.30	$249.30
Purchase #3	$41.83	4.397%	$43.6693	$43.67	$43.65	$43.70
Purchase #4	$147.95	11.837%	$165.4628	$165.46	$165.45	$165.50
Purchase #5	$26.76	7.635%	$28.8031	$28.80	$28.80	$28.80
Purchase #6	$59.63	3.823%	$61.9097	$61.91	$61.90	$61.90
Purchase #7	$106.25	3.774%	$110.2599	$110.26	$110.25	$110.30
7 purchase totals =	$682.59		$741.9921	$741.99	$741.95	$742.10