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	$81.54	11.597%	$90.9962	$91.00	$91.00	$91.00
Purchase #2	$167.98	11.813%	$187.8235	$187.82	$187.80	$187.80
Purchase #3	$247.51	9.475%	$270.9616	$270.96	$270.95	$271.00
Purchase #4	$236.97	10.712%	$262.3542	$262.35	$262.35	$262.40
Purchase #5	$68.88	13.260%	$78.0135	$78.01	$78.00	$78.00
Purchase #6	$117.98	12.315%	$132.5092	$132.51	$132.50	$132.50
Purchase #7	$207.49	11.556%	$231.4675	$231.47	$231.45	$231.50
7 purchase totals =	$1,128.35		$1,254.1257	$1,254.12	$1,254.05	$1,254.20