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	$142.33	3.421%	$147.1991	$147.20	$147.20	$147.20
Purchase #2	$204.60	6.804%	$218.521	$218.52	$218.50	$218.50
Purchase #3	$90.46	8.185%	$97.8642	$97.86	$97.85	$97.90
Purchase #4	$131.31	12.491%	$147.7119	$147.71	$147.70	$147.70
Purchase #5	$74.56	10.307%	$82.2449	$82.24	$82.25	$82.20
Purchase #6	$245.27	10.219%	$270.3341	$270.33	$270.35	$270.30
Purchase #7	$84.36	5.819%	$89.2689	$89.27	$89.25	$89.30
7 purchase totals =	$972.89		$1,053.1441	$1,053.13	$1,053.10	$1,053.10