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	$229.63	4.216%	$239.3112	$239.31	$239.30	$239.30
Purchase #2	$57.27	4.673%	$59.9462	$59.95	$59.95	$59.90
Purchase #3	$59.52	11.788%	$66.5362	$66.54	$66.55	$66.50
Purchase #4	$137.71	13.658%	$156.5184	$156.52	$156.50	$156.50
Purchase #5	$78.53	8.655%	$85.3268	$85.33	$85.35	$85.30
Purchase #6	$154.30	10.405%	$170.3549	$170.35	$170.35	$170.40
Purchase #7	$95.25	11.602%	$106.3009	$106.30	$106.30	$106.30
7 purchase totals =	$812.21		$884.2946	$884.30	$884.30	$884.20