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	$51.55	10.629%	$57.0292	$57.03	$57.05	$57.00
Purchase #2	$164.96	10.214%	$181.809	$181.81	$181.80	$181.80
Purchase #3	$74.71	11.672%	$83.4302	$83.43	$83.45	$83.40
Purchase #4	$96.98	13.309%	$109.8871	$109.89	$109.90	$109.90
Purchase #5	$84.98	4.760%	$89.025	$89.03	$89.05	$89.00
Purchase #6	$96.59	12.874%	$109.025	$109.03	$109.05	$109.00
Purchase #7	$243.85	7.534%	$262.2217	$262.22	$262.20	$262.20
7 purchase totals =	$813.62		$892.4272	$892.44	$892.50	$892.30