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	$158.81	12.797%	$179.1329	$179.13	$179.15	$179.10
Purchase #2	$51.60	11.649%	$57.6109	$57.61	$57.60	$57.60
Purchase #3	$97.63	8.520%	$105.9481	$105.95	$105.95	$105.90
Purchase #4	$82.76	8.271%	$89.6051	$89.61	$89.60	$89.60
Purchase #5	$64.59	13.570%	$73.3549	$73.35	$73.35	$73.40
Purchase #6	$51.98	6.578%	$55.3992	$55.40	$55.40	$55.40
Purchase #7	$250.96	12.779%	$283.0302	$283.03	$283.05	$283.00
7 purchase totals =	$758.33		$844.0813	$844.08	$844.10	$844.00