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	$48.84	8.148%	$52.8195	$52.82	$52.80	$52.80
Purchase #2	$183.48	3.275%	$189.489	$189.49	$189.50	$189.50
Purchase #3	$79.61	5.392%	$83.9026	$83.90	$83.90	$83.90
Purchase #4	$188.87	11.412%	$210.4238	$210.42	$210.40	$210.40
Purchase #5	$62.67	5.192%	$65.9238	$65.92	$65.90	$65.90
Purchase #6	$51.61	13.287%	$58.4674	$58.47	$58.45	$58.50
Purchase #7	$152.76	10.553%	$168.8808	$168.88	$168.90	$168.90
7 purchase totals =	$767.84		$829.9069	$829.90	$829.85	$829.90