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	$181.80	12.464%	$204.4596	$204.46	$204.45	$204.50
Purchase #2	$190.70	5.473%	$201.137	$201.14	$201.15	$201.10
Purchase #3	$55.36	7.691%	$59.6177	$59.62	$59.60	$59.60
Purchase #4	$58.29	12.844%	$65.7768	$65.78	$65.80	$65.80
Purchase #5	$137.28	7.263%	$147.2506	$147.25	$147.25	$147.30
Purchase #6	$92.95	7.522%	$99.9417	$99.94	$99.95	$99.90
Purchase #7	$55.44	8.104%	$59.9329	$59.93	$59.95	$59.90
7 purchase totals =	$771.82		$838.1163	$838.12	$838.15	$838.10