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	$8.31	6.151%	$8.8211	$8.82	$8.80	$8.80
Purchase #2	$130.95	8.223%	$141.718	$141.72	$141.70	$141.70
Purchase #3	$79.71	12.478%	$89.6562	$89.66	$89.65	$89.70
Purchase #4	$221.33	12.256%	$248.4562	$248.46	$248.45	$248.50
Purchase #5	$139.90	12.596%	$157.5218	$157.52	$157.50	$157.50
Purchase #6	$73.25	6.864%	$78.2779	$78.28	$78.30	$78.30
Purchase #7	$74.29	11.601%	$82.9084	$82.91	$82.90	$82.90
7 purchase totals =	$727.74		$807.3596	$807.37	$807.30	$807.40