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	$128.91	6.790%	$137.663	$137.66	$137.65	$137.70
Purchase #2	$78.63	4.833%	$82.4302	$82.43	$82.45	$82.40
Purchase #3	$169.90	11.219%	$188.9611	$188.96	$188.95	$189.00
Purchase #4	$97.66	9.497%	$106.9348	$106.93	$106.95	$106.90
Purchase #5	$62.98	9.733%	$69.1098	$69.11	$69.10	$69.10
Purchase #6	$131.90	9.188%	$144.019	$144.02	$144.00	$144.00
Purchase #7	$162.47	3.640%	$168.3839	$168.38	$168.40	$168.40
7 purchase totals =	$832.45		$897.5018	$897.49	$897.50	$897.50