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	$95.87	4.173%	$99.8707	$99.87	$99.85	$99.90
Purchase #2	$162.96	11.366%	$181.482	$181.48	$181.50	$181.50
Purchase #3	$122.58	7.609%	$131.9071	$131.91	$131.90	$131.90
Purchase #4	$125.37	13.357%	$142.1157	$142.12	$142.10	$142.10
Purchase #5	$140.63	10.372%	$155.2161	$155.22	$155.20	$155.20
Purchase #6	$121.31	13.791%	$138.0399	$138.04	$138.05	$138.00
Purchase #7	$156.63	3.398%	$161.9523	$161.95	$161.95	$162.00
7 purchase totals =	$925.35		$1,010.5838	$1,010.59	$1,010.55	$1,010.60