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	$84.56	6.762%	$90.2779	$90.28	$90.30	$90.30
Purchase #2	$184.72	6.584%	$196.882	$196.88	$196.90	$196.90
Purchase #3	$158.40	6.633%	$168.9067	$168.91	$168.90	$168.90
Purchase #4	$32.32	10.398%	$35.6806	$35.68	$35.70	$35.70
Purchase #5	$186.63	6.576%	$198.9028	$198.90	$198.90	$198.90
Purchase #6	$240.96	3.503%	$249.4008	$249.40	$249.40	$249.40
Purchase #7	$218.80	8.365%	$237.1026	$237.10	$237.10	$237.10
7 purchase totals =	$1,106.39		$1,177.1534	$1,177.15	$1,177.20	$1,177.20