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	$35.76	11.238%	$39.7787	$39.78	$39.80	$39.80
Purchase #2	$186.43	5.640%	$196.9447	$196.94	$196.95	$196.90
Purchase #3	$64.97	4.129%	$67.6526	$67.65	$67.65	$67.70
Purchase #4	$98.76	11.410%	$110.0285	$110.03	$110.05	$110.00
Purchase #5	$73.28	7.634%	$78.8742	$78.87	$78.85	$78.90
Purchase #6	$199.85	7.502%	$214.8427	$214.84	$214.85	$214.80
Purchase #7	$223.75	13.127%	$253.1217	$253.12	$253.10	$253.10
7 purchase totals =	$882.80		$961.2431	$961.23	$961.25	$961.20