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	$18.89	5.562%	$19.9407	$19.94	$19.95	$19.90
Purchase #2	$13.75	11.635%	$15.3498	$15.35	$15.35	$15.30
Purchase #3	$79.94	4.442%	$83.4909	$83.49	$83.50	$83.50
Purchase #4	$250.96	10.498%	$277.3058	$277.31	$277.30	$277.30
Purchase #5	$232.58	10.330%	$256.6055	$256.61	$256.60	$256.60
Purchase #6	$191.59	12.417%	$215.3797	$215.38	$215.40	$215.40
Purchase #7	$27.44	7.689%	$29.5499	$29.55	$29.55	$29.50
7 purchase totals =	$815.15		$897.6223	$897.63	$897.65	$897.50