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	$90.90	10.368%	$100.3245	$100.32	$100.30	$100.30
Purchase #2	$57.48	12.242%	$64.5167	$64.52	$64.50	$64.50
Purchase #3	$23.46	10.416%	$25.9036	$25.90	$25.90	$25.90
Purchase #4	$144.40	5.799%	$152.7738	$152.77	$152.75	$152.80
Purchase #5	$71.79	10.415%	$79.2669	$79.27	$79.25	$79.30
Purchase #6	$73.84	13.428%	$83.7552	$83.76	$83.75	$83.80
Purchase #7	$209.60	7.715%	$225.7706	$225.77	$225.75	$225.80
7 purchase totals =	$671.47		$732.3113	$732.31	$732.20	$732.40