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	$170.52	9.832%	$187.2855	$187.29	$187.30	$187.30
Purchase #2	$214.57	4.537%	$224.305	$224.31	$224.30	$224.30
Purchase #3	$39.86	3.716%	$41.3412	$41.34	$41.35	$41.30
Purchase #4	$37.37	9.417%	$40.8891	$40.89	$40.90	$40.90
Purchase #5	$233.80	3.816%	$242.7218	$242.72	$242.70	$242.70
Purchase #6	$250.37	5.764%	$264.8013	$264.80	$264.80	$264.80
Purchase #7	$43.97	3.629%	$45.5657	$45.57	$45.55	$45.60
7 purchase totals =	$990.46		$1,046.9096	$1,046.92	$1,046.90	$1,046.90