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	$57.46	4.126%	$59.8308	$59.83	$59.85	$59.80
Purchase #2	$206.56	10.727%	$228.7177	$228.72	$228.70	$228.70
Purchase #3	$136.54	3.645%	$141.5169	$141.52	$141.50	$141.50
Purchase #4	$139.90	7.297%	$150.1085	$150.11	$150.10	$150.10
Purchase #5	$16.26	6.559%	$17.3265	$17.33	$17.35	$17.30
Purchase #6	$34.36	13.203%	$38.8966	$38.90	$38.90	$38.90
Purchase #7	$150.76	3.851%	$156.5658	$156.57	$156.55	$156.60
7 purchase totals =	$741.84		$792.9628	$792.98	$792.95	$792.90