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	$126.90	12.163%	$142.3348	$142.33	$142.35	$142.30
Purchase #2	$131.67	7.196%	$141.145	$141.15	$141.15	$141.10
Purchase #3	$142.59	11.325%	$158.7383	$158.74	$158.75	$158.70
Purchase #4	$128.29	8.402%	$139.0689	$139.07	$139.05	$139.10
Purchase #5	$190.87	12.141%	$214.0435	$214.04	$214.05	$214.00
Purchase #6	$73.28	7.517%	$78.7885	$78.79	$78.80	$78.80
Purchase #7	$99.70	11.751%	$111.4157	$111.42	$111.40	$111.40
7 purchase totals =	$893.30		$985.5347	$985.54	$985.55	$985.40