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	$167.92	13.465%	$190.5304	$190.53	$190.55	$190.50
Purchase #2	$72.76	7.112%	$77.9347	$77.93	$77.95	$77.90
Purchase #3	$154.92	10.453%	$171.1138	$171.11	$171.10	$171.10
Purchase #4	$113.72	7.404%	$122.1398	$122.14	$122.15	$122.10
Purchase #5	$116.88	12.606%	$131.6139	$131.61	$131.60	$131.60
Purchase #6	$161.91	11.451%	$180.4503	$180.45	$180.45	$180.50
Purchase #7	$79.94	4.719%	$83.7124	$83.71	$83.70	$83.70
7 purchase totals =	$868.05		$957.4953	$957.48	$957.50	$957.40