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	$128.41	6.784%	$137.1213	$137.12	$137.10	$137.10
Purchase #2	$6.75	10.738%	$7.4748	$7.47	$7.45	$7.50
Purchase #3	$161.57	3.806%	$167.7194	$167.72	$167.70	$167.70
Purchase #4	$237.70	8.641%	$258.2397	$258.24	$258.25	$258.20
Purchase #5	$67.98	4.854%	$71.2797	$71.28	$71.30	$71.30
Purchase #6	$89.85	9.305%	$98.2105	$98.21	$98.20	$98.20
Purchase #7	$147.54	4.561%	$154.2693	$154.27	$154.25	$154.30
7 purchase totals =	$839.80		$894.3147	$894.31	$894.25	$894.30