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	$102.30	6.199%	$108.6416	$108.64	$108.65	$108.60
Purchase #2	$115.53	12.661%	$130.1573	$130.16	$130.15	$130.20
Purchase #3	$178.74	5.487%	$188.5475	$188.55	$188.55	$188.50
Purchase #4	$90.86	5.794%	$96.1244	$96.12	$96.10	$96.10
Purchase #5	$119.78	10.645%	$132.5306	$132.53	$132.55	$132.50
Purchase #6	$42.86	6.729%	$45.744	$45.74	$45.75	$45.70
Purchase #7	$140.54	8.474%	$152.4494	$152.45	$152.45	$152.40
7 purchase totals =	$790.61		$854.1948	$854.19	$854.20	$854.00