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	$106.78	12.670%	$120.309	$120.31	$120.30	$120.30
Purchase #2	$144.40	8.419%	$156.557	$156.56	$156.55	$156.60
Purchase #3	$142.98	3.374%	$147.8041	$147.80	$147.80	$147.80
Purchase #4	$102.64	8.457%	$111.3203	$111.32	$111.30	$111.30
Purchase #5	$178.46	3.349%	$184.4366	$184.44	$184.45	$184.40
Purchase #6	$120.84	3.363%	$124.9038	$124.90	$124.90	$124.90
Purchase #7	$224.70	13.455%	$254.9334	$254.93	$254.95	$254.90
7 purchase totals =	$1,020.80		$1,100.2642	$1,100.26	$1,100.25	$1,100.20