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	$40.79	12.313%	$45.8125	$45.81	$45.80	$45.80
Purchase #2	$90.90	8.173%	$98.3293	$98.33	$98.35	$98.30
Purchase #3	$161.27	9.807%	$177.0857	$177.09	$177.10	$177.10
Purchase #4	$154.61	5.130%	$162.5415	$162.54	$162.55	$162.50
Purchase #5	$30.64	4.793%	$32.1086	$32.11	$32.10	$32.10
Purchase #6	$196.89	11.549%	$219.6288	$219.63	$219.65	$219.60
Purchase #7	$6.56	12.562%	$7.3841	$7.38	$7.40	$7.40
7 purchase totals =	$681.66		$742.8905	$742.89	$742.95	$742.80