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	$236.51	9.528%	$259.0447	$259.04	$259.05	$259.00
Purchase #2	$244.41	10.256%	$269.4767	$269.48	$269.50	$269.50
Purchase #3	$156.59	3.646%	$162.2993	$162.30	$162.30	$162.30
Purchase #4	$39.66	9.419%	$43.3956	$43.40	$43.40	$43.40
Purchase #5	$11.77	3.328%	$12.1617	$12.16	$12.15	$12.20
Purchase #6	$83.26	7.110%	$89.1798	$89.18	$89.20	$89.20
Purchase #7	$167.85	10.574%	$185.5985	$185.60	$185.60	$185.60
7 purchase totals =	$940.05		$1,021.1563	$1,021.16	$1,021.20	$1,021.20