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	$76.69	3.197%	$79.1418	$79.14	$79.15	$79.10
Purchase #2	$13.34	10.568%	$14.7498	$14.75	$14.75	$14.70
Purchase #3	$240.31	12.630%	$270.6612	$270.66	$270.65	$270.70
Purchase #4	$35.86	5.487%	$37.8276	$37.83	$37.85	$37.80
Purchase #5	$31.33	3.556%	$32.4441	$32.44	$32.45	$32.40
Purchase #6	$56.85	5.117%	$59.759	$59.76	$59.75	$59.80
Purchase #7	$14.41	13.744%	$16.3905	$16.39	$16.40	$16.40
7 purchase totals =	$468.79		$510.9740	$510.97	$511.00	$510.90