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	$97.80	8.474%	$106.0876	$106.09	$106.10	$106.10
Purchase #2	$250.33	9.766%	$274.7772	$274.78	$274.80	$274.80
Purchase #3	$238.72	11.743%	$266.7529	$266.75	$266.75	$266.80
Purchase #4	$83.92	6.785%	$89.614	$89.61	$89.60	$89.60
Purchase #5	$41.35	4.853%	$43.3567	$43.36	$43.35	$43.40
Purchase #6	$197.82	12.629%	$222.8027	$222.80	$222.80	$222.80
Purchase #7	$232.62	12.533%	$261.7743	$261.77	$261.75	$261.80
7 purchase totals =	$1,142.56		$1,265.1654	$1,265.16	$1,265.15	$1,265.30