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	$85.95	8.797%	$93.511	$93.51	$93.50	$93.50
Purchase #2	$189.58	12.231%	$212.7675	$212.77	$212.75	$212.80
Purchase #3	$140.70	11.227%	$156.4964	$156.50	$156.50	$156.50
Purchase #4	$55.88	4.468%	$58.3767	$58.38	$58.40	$58.40
Purchase #5	$210.48	13.264%	$238.3981	$238.40	$238.40	$238.40
Purchase #6	$79.85	12.832%	$90.0964	$90.10	$90.10	$90.10
Purchase #7	$39.33	5.206%	$41.3775	$41.38	$41.40	$41.40
7 purchase totals =	$801.77		$891.0236	$891.04	$891.05	$891.10