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	$44.72	12.535%	$50.3257	$50.33	$50.35	$50.30
Purchase #2	$31.46	10.690%	$34.8231	$34.82	$34.80	$34.80
Purchase #3	$225.86	13.798%	$257.0242	$257.02	$257.00	$257.00
Purchase #4	$67.33	6.302%	$71.5731	$71.57	$71.55	$71.60
Purchase #5	$49.57	5.295%	$52.1947	$52.19	$52.20	$52.20
Purchase #6	$43.63	4.374%	$45.5384	$45.54	$45.55	$45.50
Purchase #7	$180.38	10.827%	$199.9097	$199.91	$199.90	$199.90
7 purchase totals =	$642.95		$711.3889	$711.38	$711.35	$711.30