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	$188.91	11.639%	$210.8972	$210.90	$210.90	$210.90
Purchase #2	$113.52	5.264%	$119.4957	$119.50	$119.50	$119.50
Purchase #3	$168.46	13.687%	$191.5171	$191.52	$191.50	$191.50
Purchase #4	$89.57	4.408%	$93.5182	$93.52	$93.50	$93.50
Purchase #5	$146.83	7.418%	$157.7218	$157.72	$157.70	$157.70
Purchase #6	$15.85	10.615%	$17.5325	$17.53	$17.55	$17.50
Purchase #7	$135.90	11.711%	$151.8152	$151.82	$151.80	$151.80
7 purchase totals =	$859.04		$942.4977	$942.51	$942.45	$942.40