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	$233.40	7.474%	$250.8443	$250.84	$250.85	$250.80
Purchase #2	$114.45	11.864%	$128.0283	$128.03	$128.05	$128.00
Purchase #3	$50.30	12.347%	$56.5105	$56.51	$56.50	$56.50
Purchase #4	$49.29	12.128%	$55.2679	$55.27	$55.25	$55.30
Purchase #5	$185.29	7.581%	$199.3368	$199.34	$199.35	$199.30
Purchase #6	$75.59	12.830%	$85.2882	$85.29	$85.30	$85.30
Purchase #7	$75.57	9.752%	$82.9396	$82.94	$82.95	$82.90
7 purchase totals =	$783.89		$858.2156	$858.22	$858.25	$858.10