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	$190.67	11.726%	$213.028	$213.03	$213.05	$213.00
Purchase #2	$80.69	3.781%	$83.7409	$83.74	$83.75	$83.70
Purchase #3	$88.64	11.553%	$98.8806	$98.88	$98.90	$98.90
Purchase #4	$72.53	11.214%	$80.6635	$80.66	$80.65	$80.70
Purchase #5	$203.39	7.313%	$218.2639	$218.26	$218.25	$218.30
Purchase #6	$26.37	11.873%	$29.5009	$29.50	$29.50	$29.50
Purchase #7	$79.51	13.845%	$90.5182	$90.52	$90.50	$90.50
7 purchase totals =	$741.80		$814.5960	$814.59	$814.60	$814.60