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	$80.95	3.522%	$83.8011	$83.80	$83.80	$83.80
Purchase #2	$141.46	10.814%	$156.7575	$156.76	$156.75	$156.80
Purchase #3	$103.96	4.236%	$108.3637	$108.36	$108.35	$108.40
Purchase #4	$149.32	5.408%	$157.3952	$157.40	$157.40	$157.40
Purchase #5	$30.46	4.707%	$31.8938	$31.89	$31.90	$31.90
Purchase #6	$107.82	9.824%	$118.4122	$118.41	$118.40	$118.40
Purchase #7	$177.54	7.539%	$190.9247	$190.92	$190.90	$190.90
7 purchase totals =	$791.51		$847.5482	$847.54	$847.50	$847.60