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	$73.45	12.867%	$82.9008	$82.90	$82.90	$82.90
Purchase #2	$217.34	6.636%	$231.7627	$231.76	$231.75	$231.80
Purchase #3	$7.89	10.849%	$8.746	$8.75	$8.75	$8.70
Purchase #4	$108.70	6.656%	$115.9351	$115.94	$115.95	$115.90
Purchase #5	$115.56	10.586%	$127.7932	$127.79	$127.80	$127.80
Purchase #6	$145.39	6.560%	$154.9276	$154.93	$154.95	$154.90
Purchase #7	$159.46	5.869%	$168.8187	$168.82	$168.80	$168.80
7 purchase totals =	$827.79		$890.8841	$890.89	$890.90	$890.80