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	$136.44	5.624%	$144.1134	$144.11	$144.10	$144.10
Purchase #2	$41.42	9.279%	$45.2634	$45.26	$45.25	$45.30
Purchase #3	$176.85	6.302%	$187.9951	$188.00	$188.00	$188.00
Purchase #4	$45.65	11.336%	$50.8249	$50.82	$50.80	$50.80
Purchase #5	$37.44	13.203%	$42.3832	$42.38	$42.40	$42.40
Purchase #6	$84.96	6.237%	$90.259	$90.26	$90.25	$90.30
Purchase #7	$157.29	3.458%	$162.7291	$162.73	$162.75	$162.70
7 purchase totals =	$680.05		$723.5681	$723.56	$723.55	$723.60