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	$67.77	9.811%	$74.4189	$74.42	$74.40	$74.40
Purchase #2	$155.26	10.282%	$171.2238	$171.22	$171.20	$171.20
Purchase #3	$85.25	4.746%	$89.296	$89.30	$89.30	$89.30
Purchase #4	$92.57	12.772%	$104.393	$104.39	$104.40	$104.40
Purchase #5	$190.45	10.473%	$210.3958	$210.40	$210.40	$210.40
Purchase #6	$242.45	8.703%	$263.5504	$263.55	$263.55	$263.60
Purchase #7	$64.33	4.192%	$67.0267	$67.03	$67.05	$67.00
7 purchase totals =	$898.08		$980.3046	$980.31	$980.30	$980.30