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	$80.91	12.492%	$91.0173	$91.02	$91.00	$91.00
Purchase #2	$80.58	6.193%	$85.5703	$85.57	$85.55	$85.60
Purchase #3	$197.94	12.530%	$222.7419	$222.74	$222.75	$222.70
Purchase #4	$155.74	4.620%	$162.9352	$162.94	$162.95	$162.90
Purchase #5	$103.52	7.497%	$111.2809	$111.28	$111.30	$111.30
Purchase #6	$213.44	3.802%	$221.555	$221.56	$221.55	$221.60
Purchase #7	$120.41	12.651%	$135.6431	$135.64	$135.65	$135.60
7 purchase totals =	$952.54		$1,030.7437	$1,030.75	$1,030.75	$1,030.70