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	$199.84	11.866%	$223.553	$223.55	$223.55	$223.60
Purchase #2	$171.98	6.240%	$182.7116	$182.71	$182.70	$182.70
Purchase #3	$78.32	5.637%	$82.7349	$82.73	$82.75	$82.70
Purchase #4	$209.98	13.356%	$238.0249	$238.02	$238.00	$238.00
Purchase #5	$43.71	7.267%	$46.8864	$46.89	$46.90	$46.90
Purchase #6	$139.87	8.807%	$152.1884	$152.19	$152.20	$152.20
Purchase #7	$169.37	10.410%	$187.0014	$187.00	$187.00	$187.00
7 purchase totals =	$1,013.07		$1,113.1006	$1,113.09	$1,113.10	$1,113.10