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	$146.82	8.797%	$159.7358	$159.74	$159.75	$159.70
Purchase #2	$82.91	6.788%	$88.5379	$88.54	$88.55	$88.50
Purchase #3	$84.61	10.142%	$93.1911	$93.19	$93.20	$93.20
Purchase #4	$92.46	8.626%	$100.4356	$100.44	$100.45	$100.40
Purchase #5	$36.69	3.322%	$37.9088	$37.91	$37.90	$37.90
Purchase #6	$82.27	3.312%	$84.9948	$84.99	$85.00	$85.00
Purchase #7	$90.68	10.651%	$100.3383	$100.34	$100.35	$100.30
7 purchase totals =	$616.44		$665.1423	$665.15	$665.20	$665.00