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	$81.60	10.347%	$90.0432	$90.04	$90.05	$90.00
Purchase #2	$201.73	4.284%	$210.3721	$210.37	$210.35	$210.40
Purchase #3	$129.86	12.446%	$146.0224	$146.02	$146.00	$146.00
Purchase #4	$39.82	6.292%	$42.3255	$42.33	$42.35	$42.30
Purchase #5	$79.31	3.412%	$82.0161	$82.02	$82.00	$82.00
Purchase #6	$76.95	3.870%	$79.928	$79.93	$79.95	$79.90
Purchase #7	$151.44	3.537%	$156.7964	$156.80	$156.80	$156.80
7 purchase totals =	$760.71		$807.5037	$807.51	$807.50	$807.40