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	$243.42	11.254%	$270.8145	$270.81	$270.80	$270.80
Purchase #2	$148.88	11.440%	$165.9119	$165.91	$165.90	$165.90
Purchase #3	$198.59	11.334%	$221.0982	$221.10	$221.10	$221.10
Purchase #4	$150.54	9.304%	$164.5462	$164.55	$164.55	$164.50
Purchase #5	$88.95	11.106%	$98.8288	$98.83	$98.85	$98.80
Purchase #6	$107.73	5.357%	$113.5011	$113.50	$113.50	$113.50
Purchase #7	$5.28	8.874%	$5.7485	$5.75	$5.75	$5.70
7 purchase totals =	$943.39		$1,040.4492	$1,040.45	$1,040.45	$1,040.30