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	$109.48	10.807%	$121.3115	$121.31	$121.30	$121.30
Purchase #2	$112.53	10.301%	$124.1217	$124.12	$124.10	$124.10
Purchase #3	$7.70	10.653%	$8.5203	$8.52	$8.50	$8.50
Purchase #4	$49.34	4.493%	$51.5568	$51.56	$51.55	$51.60
Purchase #5	$141.38	4.350%	$147.53	$147.53	$147.55	$147.50
Purchase #6	$25.89	13.199%	$29.3072	$29.31	$29.30	$29.30
Purchase #7	$79.58	12.857%	$89.8116	$89.81	$89.80	$89.80
7 purchase totals =	$525.90		$572.1591	$572.16	$572.10	$572.10