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	$36.34	11.267%	$40.4344	$40.43	$40.45	$40.40
Purchase #2	$139.84	7.187%	$149.8903	$149.89	$149.90	$149.90
Purchase #3	$37.49	13.558%	$42.5729	$42.57	$42.55	$42.60
Purchase #4	$169.38	11.260%	$188.4522	$188.45	$188.45	$188.50
Purchase #5	$33.63	9.135%	$36.7021	$36.70	$36.70	$36.70
Purchase #6	$123.45	7.557%	$132.7791	$132.78	$132.80	$132.80
Purchase #7	$103.74	12.421%	$116.6255	$116.63	$116.65	$116.60
7 purchase totals =	$643.87		$707.4565	$707.45	$707.50	$707.50