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	$126.76	7.365%	$136.0959	$136.10	$136.10	$136.10
Purchase #2	$40.33	4.585%	$42.1791	$42.18	$42.20	$42.20
Purchase #3	$39.98	9.363%	$43.7233	$43.72	$43.70	$43.70
Purchase #4	$217.46	7.238%	$233.1998	$233.20	$233.20	$233.20
Purchase #5	$156.27	6.110%	$165.8181	$165.82	$165.80	$165.80
Purchase #6	$88.89	10.452%	$98.1808	$98.18	$98.20	$98.20
Purchase #7	$23.98	13.144%	$27.1319	$27.13	$27.15	$27.10
7 purchase totals =	$693.67		$746.3289	$746.33	$746.35	$746.30