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	$94.89	4.727%	$99.3755	$99.38	$99.40	$99.40
Purchase #2	$55.59	4.270%	$57.9637	$57.96	$57.95	$58.00
Purchase #3	$214.87	12.300%	$241.299	$241.30	$241.30	$241.30
Purchase #4	$92.79	7.238%	$99.5061	$99.51	$99.50	$99.50
Purchase #5	$210.25	11.316%	$234.0419	$234.04	$234.05	$234.00
Purchase #6	$59.28	6.284%	$63.0052	$63.01	$63.00	$63.00
Purchase #7	$159.28	13.708%	$181.1141	$181.11	$181.10	$181.10
7 purchase totals =	$886.95		$976.3055	$976.31	$976.30	$976.30