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	$215.45	13.803%	$245.1886	$245.19	$245.20	$245.20
Purchase #2	$205.27	10.817%	$227.4741	$227.47	$227.45	$227.50
Purchase #3	$207.53	12.508%	$233.4879	$233.49	$233.50	$233.50
Purchase #4	$175.91	5.446%	$185.4901	$185.49	$185.50	$185.50
Purchase #5	$43.35	8.225%	$46.9155	$46.92	$46.90	$46.90
Purchase #6	$197.82	12.180%	$221.9145	$221.91	$221.90	$221.90
Purchase #7	$170.32	5.317%	$179.3759	$179.38	$179.40	$179.40
7 purchase totals =	$1,215.65		$1,339.8466	$1,339.85	$1,339.85	$1,339.90