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	$27.66	12.751%	$31.1869	$31.19	$31.20	$31.20
Purchase #2	$216.47	6.725%	$231.0276	$231.03	$231.05	$231.00
Purchase #3	$174.97	5.277%	$184.2032	$184.20	$184.20	$184.20
Purchase #4	$164.55	13.826%	$187.3007	$187.30	$187.30	$187.30
Purchase #5	$145.56	11.687%	$162.5716	$162.57	$162.55	$162.60
Purchase #6	$40.40	4.640%	$42.2746	$42.27	$42.25	$42.30
Purchase #7	$133.78	4.735%	$140.1145	$140.11	$140.10	$140.10
7 purchase totals =	$903.39		$978.6791	$978.67	$978.65	$978.70