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	$54.85	4.866%	$57.519	$57.52	$57.50	$57.50
Purchase #2	$171.48	6.562%	$182.7325	$182.73	$182.75	$182.70
Purchase #3	$216.79	5.862%	$229.4982	$229.50	$229.50	$229.50
Purchase #4	$58.27	5.319%	$61.3694	$61.37	$61.35	$61.40
Purchase #5	$43.75	9.779%	$48.0283	$48.03	$48.05	$48.00
Purchase #6	$48.33	13.506%	$54.8574	$54.86	$54.85	$54.90
Purchase #7	$108.49	4.109%	$112.9479	$112.95	$112.95	$112.90
7 purchase totals =	$701.96		$746.9527	$746.96	$746.95	$746.90