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	$133.54	5.570%	$140.9782	$140.98	$141.00	$141.00
Purchase #2	$181.97	7.499%	$195.6159	$195.62	$195.60	$195.60
Purchase #3	$161.91	7.791%	$174.5244	$174.52	$174.50	$174.50
Purchase #4	$211.64	7.444%	$227.3945	$227.39	$227.40	$227.40
Purchase #5	$196.53	6.135%	$208.5871	$208.59	$208.60	$208.60
Purchase #6	$35.90	11.122%	$39.8928	$39.89	$39.90	$39.90
Purchase #7	$100.77	4.769%	$105.5757	$105.58	$105.60	$105.60
7 purchase totals =	$1,022.26		$1,092.5686	$1,092.57	$1,092.60	$1,092.60