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	$171.66	4.471%	$179.3349	$179.33	$179.35	$179.30
Purchase #2	$140.42	6.129%	$149.0263	$149.03	$149.05	$149.00
Purchase #3	$82.91	9.247%	$90.5767	$90.58	$90.60	$90.60
Purchase #4	$99.27	3.802%	$103.0442	$103.04	$103.05	$103.00
Purchase #5	$80.97	7.357%	$86.927	$86.93	$86.95	$86.90
Purchase #6	$190.72	7.430%	$204.8905	$204.89	$204.90	$204.90
Purchase #7	$67.38	9.474%	$73.7636	$73.76	$73.75	$73.80
7 purchase totals =	$833.33		$887.5632	$887.56	$887.65	$887.50