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	$98.33	8.689%	$106.8739	$106.87	$106.85	$106.90
Purchase #2	$155.38	11.296%	$172.9317	$172.93	$172.95	$172.90
Purchase #3	$62.52	6.517%	$66.5944	$66.59	$66.60	$66.60
Purchase #4	$147.59	5.709%	$156.0159	$156.02	$156.00	$156.00
Purchase #5	$18.85	11.596%	$21.0358	$21.04	$21.05	$21.00
Purchase #6	$110.53	7.429%	$118.7413	$118.74	$118.75	$118.70
Purchase #7	$135.31	11.541%	$150.9261	$150.93	$150.95	$150.90
7 purchase totals =	$728.51		$793.1191	$793.12	$793.15	$793.00