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	$124.36	13.292%	$140.8899	$140.89	$140.90	$140.90
Purchase #2	$143.74	4.846%	$150.7056	$150.71	$150.70	$150.70
Purchase #3	$198.46	10.789%	$219.8718	$219.87	$219.85	$219.90
Purchase #4	$62.27	11.299%	$69.3059	$69.31	$69.30	$69.30
Purchase #5	$67.37	6.477%	$71.7336	$71.73	$71.75	$71.70
Purchase #6	$187.27	12.540%	$210.7537	$210.75	$210.75	$210.80
Purchase #7	$156.96	9.770%	$172.295	$172.30	$172.30	$172.30
7 purchase totals =	$940.43		$1,035.5555	$1,035.56	$1,035.55	$1,035.60