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	$235.83	12.541%	$265.4054	$265.41	$265.40	$265.40
Purchase #2	$84.82	7.471%	$91.1569	$91.16	$91.15	$91.20
Purchase #3	$222.74	10.814%	$246.8271	$246.83	$246.85	$246.80
Purchase #4	$76.82	5.296%	$80.8884	$80.89	$80.90	$80.90
Purchase #5	$80.58	11.674%	$89.9869	$89.99	$90.00	$90.00
Purchase #6	$46.56	13.554%	$52.8707	$52.87	$52.85	$52.90
Purchase #7	$156.26	5.296%	$164.5355	$164.54	$164.55	$164.50
7 purchase totals =	$903.61		$991.6709	$991.69	$991.70	$991.70