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	$88.27	5.260%	$92.913	$92.91	$92.90	$92.90
Purchase #2	$122.92	6.387%	$130.7709	$130.77	$130.75	$130.80
Purchase #3	$174.29	12.762%	$196.5329	$196.53	$196.55	$196.50
Purchase #4	$88.98	6.858%	$95.0822	$95.08	$95.10	$95.10
Purchase #5	$210.38	7.130%	$225.3801	$225.38	$225.40	$225.40
Purchase #6	$108.84	10.497%	$120.2649	$120.26	$120.25	$120.30
Purchase #7	$81.43	10.290%	$89.8091	$89.81	$89.80	$89.80
7 purchase totals =	$875.11		$950.7531	$950.74	$950.75	$950.80