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	$234.70	9.429%	$256.8299	$256.83	$256.85	$256.80
Purchase #2	$213.69	13.777%	$243.1301	$243.13	$243.15	$243.10
Purchase #3	$41.41	9.458%	$45.3266	$45.33	$45.35	$45.30
Purchase #4	$202.55	9.675%	$222.1467	$222.15	$222.15	$222.10
Purchase #5	$21.81	3.462%	$22.5651	$22.57	$22.55	$22.60
Purchase #6	$167.29	10.550%	$184.9391	$184.94	$184.95	$184.90
Purchase #7	$35.57	13.435%	$40.3488	$40.35	$40.35	$40.30
7 purchase totals =	$917.02		$1,015.2863	$1,015.30	$1,015.35	$1,015.10