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	$46.55	12.485%	$52.3618	$52.36	$52.35	$52.40
Purchase #2	$132.65	4.427%	$138.5224	$138.52	$138.50	$138.50
Purchase #3	$211.32	8.820%	$229.9584	$229.96	$229.95	$230.00
Purchase #4	$179.78	6.179%	$190.8886	$190.89	$190.90	$190.90
Purchase #5	$42.55	12.562%	$47.8951	$47.90	$47.90	$47.90
Purchase #6	$192.92	7.270%	$206.9453	$206.95	$206.95	$206.90
Purchase #7	$89.49	11.764%	$100.0176	$100.02	$100.00	$100.00
7 purchase totals =	$895.26		$966.5892	$966.60	$966.55	$966.60