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	$35.36	5.289%	$37.2302	$37.23	$37.25	$37.20
Purchase #2	$157.86	6.605%	$168.2867	$168.29	$168.30	$168.30
Purchase #3	$68.94	7.474%	$74.0926	$74.09	$74.10	$74.10
Purchase #4	$98.33	13.195%	$111.3046	$111.30	$111.30	$111.30
Purchase #5	$249.79	12.141%	$280.117	$280.12	$280.10	$280.10
Purchase #6	$85.57	11.228%	$95.1778	$95.18	$95.20	$95.20
Purchase #7	$130.94	11.727%	$146.2953	$146.30	$146.30	$146.30
7 purchase totals =	$826.79		$912.5042	$912.51	$912.55	$912.50