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	$6.29	9.385%	$6.8803	$6.88	$6.90	$6.90
Purchase #2	$68.38	5.334%	$72.0274	$72.03	$72.05	$72.00
Purchase #3	$163.37	3.150%	$168.5162	$168.52	$168.50	$168.50
Purchase #4	$233.76	7.237%	$250.6772	$250.68	$250.70	$250.70
Purchase #5	$83.88	6.510%	$89.3406	$89.34	$89.35	$89.30
Purchase #6	$241.58	5.166%	$254.06	$254.06	$254.05	$254.10
Purchase #7	$199.30	11.869%	$222.9549	$222.95	$222.95	$223.00
7 purchase totals =	$996.56		$1,064.4566	$1,064.46	$1,064.50	$1,064.50