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	$186.99	6.700%	$199.5183	$199.52	$199.50	$199.50
Purchase #2	$247.94	6.616%	$264.3437	$264.34	$264.35	$264.30
Purchase #3	$104.71	4.599%	$109.5256	$109.53	$109.55	$109.50
Purchase #4	$29.31	12.709%	$33.035	$33.04	$33.05	$33.00
Purchase #5	$77.95	6.278%	$82.8437	$82.84	$82.85	$82.80
Purchase #6	$78.61	5.227%	$82.7189	$82.72	$82.70	$82.70
Purchase #7	$148.27	4.562%	$155.0341	$155.03	$155.05	$155.00
7 purchase totals =	$873.78		$927.0193	$927.02	$927.05	$926.80