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	$80.53	12.132%	$90.2999	$90.30	$90.30	$90.30
Purchase #2	$35.74	11.804%	$39.9587	$39.96	$39.95	$40.00
Purchase #3	$87.94	6.345%	$93.5198	$93.52	$93.50	$93.50
Purchase #4	$196.43	11.131%	$218.2946	$218.29	$218.30	$218.30
Purchase #5	$96.61	8.821%	$105.132	$105.13	$105.15	$105.10
Purchase #6	$249.66	7.836%	$269.2234	$269.22	$269.20	$269.20
Purchase #7	$194.27	7.135%	$208.1312	$208.13	$208.15	$208.10
7 purchase totals =	$941.18		$1,024.5596	$1,024.55	$1,024.55	$1,024.50