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	$148.96	12.846%	$168.0954	$168.10	$168.10	$168.10
Purchase #2	$238.33	8.385%	$258.314	$258.31	$258.30	$258.30
Purchase #3	$115.29	10.625%	$127.5396	$127.54	$127.55	$127.50
Purchase #4	$129.58	10.214%	$142.8153	$142.82	$142.80	$142.80
Purchase #5	$190.68	12.380%	$214.2862	$214.29	$214.30	$214.30
Purchase #6	$109.79	6.785%	$117.2393	$117.24	$117.25	$117.20
Purchase #7	$249.28	8.659%	$270.8652	$270.87	$270.85	$270.90
7 purchase totals =	$1,181.91		$1,299.1550	$1,299.17	$1,299.15	$1,299.10