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	$14.27	5.793%	$15.0967	$15.10	$15.10	$15.10
Purchase #2	$223.96	8.627%	$243.281	$243.28	$243.30	$243.30
Purchase #3	$193.45	11.606%	$215.9018	$215.90	$215.90	$215.90
Purchase #4	$78.52	5.695%	$82.9917	$82.99	$83.00	$83.00
Purchase #5	$189.44	13.805%	$215.5922	$215.59	$215.60	$215.60
Purchase #6	$136.73	13.850%	$155.6671	$155.67	$155.65	$155.70
Purchase #7	$167.41	4.307%	$174.6203	$174.62	$174.60	$174.60
7 purchase totals =	$1,003.78		$1,103.1508	$1,103.15	$1,103.15	$1,103.20