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	$28.60	11.206%	$31.8049	$31.80	$31.80	$31.80
Purchase #2	$168.85	5.787%	$178.6213	$178.62	$178.60	$178.60
Purchase #3	$86.54	13.539%	$98.2567	$98.26	$98.25	$98.30
Purchase #4	$180.61	4.163%	$188.1288	$188.13	$188.15	$188.10
Purchase #5	$26.86	12.268%	$30.1552	$30.16	$30.15	$30.20
Purchase #6	$229.58	11.323%	$255.5753	$255.58	$255.60	$255.60
Purchase #7	$239.67	4.428%	$250.2826	$250.28	$250.30	$250.30
7 purchase totals =	$960.71		$1,032.8248	$1,032.83	$1,032.85	$1,032.90