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	$123.94	8.650%	$134.6608	$134.66	$134.65	$134.70
Purchase #2	$50.72	3.822%	$52.6585	$52.66	$52.65	$52.70
Purchase #3	$165.65	4.862%	$173.7039	$173.70	$173.70	$173.70
Purchase #4	$81.67	9.719%	$89.6075	$89.61	$89.60	$89.60
Purchase #5	$82.76	3.117%	$85.3396	$85.34	$85.35	$85.30
Purchase #6	$152.75	12.529%	$171.888	$171.89	$171.90	$171.90
Purchase #7	$165.56	3.348%	$171.1029	$171.10	$171.10	$171.10
7 purchase totals =	$823.05		$878.9612	$878.96	$878.95	$879.00