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	$77.60	6.263%	$82.4601	$82.46	$82.45	$82.50
Purchase #2	$106.32	9.637%	$116.5661	$116.57	$116.55	$116.60
Purchase #3	$46.74	4.677%	$48.926	$48.93	$48.95	$48.90
Purchase #4	$63.85	12.622%	$71.9091	$71.91	$71.90	$71.90
Purchase #5	$79.38	11.208%	$88.2769	$88.28	$88.30	$88.30
Purchase #6	$78.94	9.779%	$86.6595	$86.66	$86.65	$86.70
Purchase #7	$23.70	7.641%	$25.5109	$25.51	$25.50	$25.50
7 purchase totals =	$476.53		$520.3086	$520.32	$520.30	$520.40