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	$112.40	3.414%	$116.2373	$116.24	$116.25	$116.20
Purchase #2	$144.40	5.471%	$152.3001	$152.30	$152.30	$152.30
Purchase #3	$39.83	13.482%	$45.1999	$45.20	$45.20	$45.20
Purchase #4	$128.46	9.308%	$140.4171	$140.42	$140.40	$140.40
Purchase #5	$15.59	11.494%	$17.3819	$17.38	$17.40	$17.40
Purchase #6	$238.71	10.413%	$263.5669	$263.57	$263.55	$263.60
Purchase #7	$239.27	10.681%	$264.8264	$264.83	$264.85	$264.80
7 purchase totals =	$918.66		$999.9296	$999.94	$999.95	$999.90