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	$98.89	12.570%	$111.3205	$111.32	$111.30	$111.30
Purchase #2	$125.36	13.678%	$142.5067	$142.51	$142.50	$142.50
Purchase #3	$84.52	13.686%	$96.0874	$96.09	$96.10	$96.10
Purchase #4	$187.41	13.427%	$212.5735	$212.57	$212.55	$212.60
Purchase #5	$84.51	5.151%	$88.8631	$88.86	$88.85	$88.90
Purchase #6	$120.26	5.343%	$126.6855	$126.69	$126.70	$126.70
Purchase #7	$48.32	13.342%	$54.7669	$54.77	$54.75	$54.80
7 purchase totals =	$749.27		$832.8036	$832.81	$832.75	$832.90