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	$89.84	13.375%	$101.8561	$101.86	$101.85	$101.90
Purchase #2	$109.56	3.809%	$113.7331	$113.73	$113.75	$113.70
Purchase #3	$105.82	8.294%	$114.5967	$114.60	$114.60	$114.60
Purchase #4	$162.93	11.406%	$181.5138	$181.51	$181.50	$181.50
Purchase #5	$145.98	12.422%	$164.1136	$164.11	$164.10	$164.10
Purchase #6	$7.83	6.133%	$8.3102	$8.31	$8.30	$8.30
Purchase #7	$123.25	6.546%	$131.3179	$131.32	$131.30	$131.30
7 purchase totals =	$745.21		$815.4414	$815.44	$815.40	$815.40