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	$75.76	9.151%	$82.6928	$82.69	$82.70	$82.70
Purchase #2	$218.78	12.486%	$246.0969	$246.10	$246.10	$246.10
Purchase #3	$151.25	11.354%	$168.4229	$168.42	$168.40	$168.40
Purchase #4	$67.95	7.124%	$72.7908	$72.79	$72.80	$72.80
Purchase #5	$96.60	9.300%	$105.5838	$105.58	$105.60	$105.60
Purchase #6	$26.34	3.830%	$27.3488	$27.35	$27.35	$27.30
Purchase #7	$165.33	7.262%	$177.3363	$177.34	$177.35	$177.30
7 purchase totals =	$802.01		$880.2723	$880.27	$880.30	$880.20