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	$187.36	6.413%	$199.3754	$199.38	$199.40	$199.40
Purchase #2	$72.73	13.360%	$82.4467	$82.45	$82.45	$82.40
Purchase #3	$119.40	3.245%	$123.2745	$123.27	$123.25	$123.30
Purchase #4	$196.47	10.835%	$217.7575	$217.76	$217.75	$217.80
Purchase #5	$115.64	11.614%	$129.0704	$129.07	$129.05	$129.10
Purchase #6	$38.64	11.638%	$43.1369	$43.14	$43.15	$43.10
Purchase #7	$230.56	6.251%	$244.9723	$244.97	$244.95	$245.00
7 purchase totals =	$960.80		$1,040.0337	$1,040.04	$1,040.00	$1,040.10