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	$96.76	3.217%	$99.8728	$99.87	$99.85	$99.90
Purchase #2	$141.88	10.873%	$157.3066	$157.31	$157.30	$157.30
Purchase #3	$22.64	11.199%	$25.1755	$25.18	$25.20	$25.20
Purchase #4	$41.49	7.549%	$44.6221	$44.62	$44.60	$44.60
Purchase #5	$192.87	3.490%	$199.6012	$199.60	$199.60	$199.60
Purchase #6	$51.43	10.617%	$56.8903	$56.89	$56.90	$56.90
Purchase #7	$79.80	12.290%	$89.6074	$89.61	$89.60	$89.60
7 purchase totals =	$626.87		$673.0759	$673.08	$673.05	$673.10