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	$85.97	4.601%	$89.9255	$89.93	$89.95	$89.90
Purchase #2	$221.69	8.469%	$240.4649	$240.46	$240.45	$240.50
Purchase #3	$74.30	5.488%	$78.3776	$78.38	$78.40	$78.40
Purchase #4	$27.44	6.858%	$29.3218	$29.32	$29.30	$29.30
Purchase #5	$43.32	7.394%	$46.5231	$46.52	$46.50	$46.50
Purchase #6	$234.78	5.871%	$248.5639	$248.56	$248.55	$248.60
Purchase #7	$125.32	12.342%	$140.787	$140.79	$140.80	$140.80
7 purchase totals =	$812.82		$873.9638	$873.96	$873.95	$874.00