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	$89.45	5.794%	$94.6327	$94.63	$94.65	$94.60
Purchase #2	$170.56	4.156%	$177.6485	$177.65	$177.65	$177.60
Purchase #3	$171.68	9.410%	$187.8351	$187.84	$187.85	$187.80
Purchase #4	$247.34	11.743%	$276.3851	$276.39	$276.40	$276.40
Purchase #5	$55.38	10.796%	$61.3588	$61.36	$61.35	$61.40
Purchase #6	$197.51	13.357%	$223.8914	$223.89	$223.90	$223.90
Purchase #7	$52.63	12.530%	$59.2245	$59.22	$59.20	$59.20
7 purchase totals =	$984.55		$1,080.9761	$1,080.98	$1,081.00	$1,080.90