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	$223.34	8.276%	$241.8236	$241.82	$241.80	$241.80
Purchase #2	$83.87	6.241%	$89.1043	$89.10	$89.10	$89.10
Purchase #3	$102.92	11.477%	$114.7321	$114.73	$114.75	$114.70
Purchase #4	$105.66	8.171%	$114.2935	$114.29	$114.30	$114.30
Purchase #5	$25.90	5.805%	$27.4035	$27.40	$27.40	$27.40
Purchase #6	$78.51	8.583%	$85.2485	$85.25	$85.25	$85.20
Purchase #7	$148.31	6.358%	$157.7395	$157.74	$157.75	$157.70
7 purchase totals =	$768.51		$830.3450	$830.33	$830.35	$830.20