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	$222.77	12.393%	$250.3779	$250.38	$250.40	$250.40
Purchase #2	$180.97	10.242%	$199.5049	$199.50	$199.50	$199.50
Purchase #3	$11.88	10.492%	$13.1264	$13.13	$13.15	$13.10
Purchase #4	$128.26	9.774%	$140.7961	$140.80	$140.80	$140.80
Purchase #5	$190.30	5.380%	$200.5381	$200.54	$200.55	$200.50
Purchase #6	$45.88	9.574%	$50.2726	$50.27	$50.25	$50.30
Purchase #7	$147.43	5.413%	$155.4104	$155.41	$155.40	$155.40
7 purchase totals =	$927.49		$1,010.0264	$1,010.03	$1,010.05	$1,010.00