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	$21.46	3.784%	$22.272	$22.27	$22.25	$22.30
Purchase #2	$159.25	9.434%	$174.2736	$174.27	$174.25	$174.30
Purchase #3	$96.30	8.612%	$104.5934	$104.59	$104.60	$104.60
Purchase #4	$162.40	5.161%	$170.7815	$170.78	$170.80	$170.80
Purchase #5	$173.93	10.329%	$191.8952	$191.90	$191.90	$191.90
Purchase #6	$224.57	12.874%	$253.4811	$253.48	$253.50	$253.50
Purchase #7	$88.83	11.524%	$99.0668	$99.07	$99.05	$99.10
7 purchase totals =	$926.74		$1,016.3636	$1,016.36	$1,016.35	$1,016.50