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	$128.32	4.697%	$134.3472	$134.35	$134.35	$134.30
Purchase #2	$245.94	7.473%	$264.3191	$264.32	$264.30	$264.30
Purchase #3	$21.43	11.308%	$23.8533	$23.85	$23.85	$23.90
Purchase #4	$10.67	9.129%	$11.6441	$11.64	$11.65	$11.60
Purchase #5	$55.62	10.262%	$61.3277	$61.33	$61.35	$61.30
Purchase #6	$248.91	10.524%	$275.1053	$275.11	$275.10	$275.10
Purchase #7	$94.98	5.299%	$100.013	$100.01	$100.00	$100.00
7 purchase totals =	$805.87		$870.6097	$870.61	$870.60	$870.50