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	$72.43	11.453%	$80.7254	$80.73	$80.75	$80.70
Purchase #2	$33.76	4.495%	$35.2775	$35.28	$35.30	$35.30
Purchase #3	$182.64	7.789%	$196.8658	$196.87	$196.85	$196.90
Purchase #4	$216.46	13.591%	$245.8791	$245.88	$245.90	$245.90
Purchase #5	$16.87	6.598%	$17.9831	$17.98	$18.00	$18.00
Purchase #6	$121.88	3.860%	$126.5846	$126.58	$126.60	$126.60
Purchase #7	$25.55	12.805%	$28.8217	$28.82	$28.80	$28.80
7 purchase totals =	$669.59		$732.1372	$732.14	$732.20	$732.20