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	$89.45	11.282%	$99.5417	$99.54	$99.55	$99.50
Purchase #2	$145.58	7.368%	$156.3063	$156.31	$156.30	$156.30
Purchase #3	$187.85	10.566%	$207.6982	$207.70	$207.70	$207.70
Purchase #4	$86.80	7.825%	$93.5921	$93.59	$93.60	$93.60
Purchase #5	$153.52	4.148%	$159.888	$159.89	$159.90	$159.90
Purchase #6	$30.44	4.534%	$31.8201	$31.82	$31.80	$31.80
Purchase #7	$132.82	6.816%	$141.873	$141.87	$141.85	$141.90
7 purchase totals =	$826.46		$890.7194	$890.72	$890.70	$890.70