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	$133.31	13.696%	$151.5681	$151.57	$151.55	$151.60
Purchase #2	$81.63	10.338%	$90.0689	$90.07	$90.05	$90.10
Purchase #3	$54.77	10.704%	$60.6326	$60.63	$60.65	$60.60
Purchase #4	$58.37	6.807%	$62.3432	$62.34	$62.35	$62.30
Purchase #5	$166.74	6.443%	$177.4831	$177.48	$177.50	$177.50
Purchase #6	$145.93	5.349%	$153.7358	$153.74	$153.75	$153.70
Purchase #7	$84.38	6.112%	$89.5373	$89.54	$89.55	$89.50
7 purchase totals =	$725.13		$785.3690	$785.37	$785.40	$785.30