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	$173.35	4.140%	$180.5267	$180.53	$180.55	$180.50
Purchase #2	$245.91	11.460%	$274.0913	$274.09	$274.10	$274.10
Purchase #3	$114.54	12.862%	$129.2721	$129.27	$129.25	$129.30
Purchase #4	$85.25	6.415%	$90.7188	$90.72	$90.70	$90.70
Purchase #5	$102.64	10.553%	$113.4716	$113.47	$113.45	$113.50
Purchase #6	$6.89	13.436%	$7.8157	$7.82	$7.80	$7.80
Purchase #7	$221.91	8.188%	$240.08	$240.08	$240.10	$240.10
7 purchase totals =	$950.49		$1,035.9762	$1,035.98	$1,035.95	$1,036.00