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	$174.99	5.849%	$185.2252	$185.23	$185.25	$185.20
Purchase #2	$75.57	12.563%	$85.0639	$85.06	$85.05	$85.10
Purchase #3	$88.89	12.415%	$99.9257	$99.93	$99.95	$99.90
Purchase #4	$114.84	5.211%	$120.8243	$120.82	$120.80	$120.80
Purchase #5	$158.54	13.143%	$179.3769	$179.38	$179.40	$179.40
Purchase #6	$177.82	9.241%	$194.2523	$194.25	$194.25	$194.30
Purchase #7	$37.97	10.185%	$41.8372	$41.84	$41.85	$41.80
7 purchase totals =	$828.62		$906.5055	$906.51	$906.55	$906.50