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	$169.97	4.326%	$177.3229	$177.32	$177.30	$177.30
Purchase #2	$57.62	7.240%	$61.7917	$61.79	$61.80	$61.80
Purchase #3	$227.65	12.676%	$256.5069	$256.51	$256.50	$256.50
Purchase #4	$210.96	11.155%	$234.4926	$234.49	$234.50	$234.50
Purchase #5	$63.51	7.845%	$68.4924	$68.49	$68.50	$68.50
Purchase #6	$51.40	6.780%	$54.8849	$54.88	$54.90	$54.90
Purchase #7	$131.66	12.327%	$147.8897	$147.89	$147.90	$147.90
7 purchase totals =	$912.77		$1,001.3811	$1,001.37	$1,001.40	$1,001.40