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	$37.34	8.705%	$40.5904	$40.59	$40.60	$40.60
Purchase #2	$194.27	4.658%	$203.3191	$203.32	$203.30	$203.30
Purchase #3	$136.91	3.596%	$141.8333	$141.83	$141.85	$141.80
Purchase #4	$153.39	12.193%	$172.0928	$172.09	$172.10	$172.10
Purchase #5	$142.79	8.653%	$155.1456	$155.15	$155.15	$155.10
Purchase #6	$54.47	8.796%	$59.2612	$59.26	$59.25	$59.30
Purchase #7	$73.56	10.276%	$81.119	$81.12	$81.10	$81.10
7 purchase totals =	$792.73		$853.3614	$853.36	$853.35	$853.30