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	$240.94	12.481%	$271.0117	$271.01	$271.00	$271.00
Purchase #2	$183.81	8.718%	$199.8346	$199.83	$199.85	$199.80
Purchase #3	$96.29	3.295%	$99.4628	$99.46	$99.45	$99.50
Purchase #4	$66.45	7.427%	$71.3852	$71.39	$71.40	$71.40
Purchase #5	$25.76	6.181%	$27.3522	$27.35	$27.35	$27.40
Purchase #6	$86.48	11.402%	$96.3404	$96.34	$96.35	$96.30
Purchase #7	$141.63	8.833%	$154.1402	$154.14	$154.15	$154.10
7 purchase totals =	$841.36		$919.5271	$919.52	$919.55	$919.50