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	$35.81	10.288%	$39.4941	$39.49	$39.50	$39.50
Purchase #2	$83.70	13.632%	$95.11	$95.11	$95.10	$95.10
Purchase #3	$198.46	12.343%	$222.9559	$222.96	$222.95	$223.00
Purchase #4	$125.43	12.429%	$141.0197	$141.02	$141.00	$141.00
Purchase #5	$144.51	13.841%	$164.5116	$164.51	$164.50	$164.50
Purchase #6	$72.49	3.412%	$74.9634	$74.96	$74.95	$75.00
Purchase #7	$79.56	8.581%	$86.387	$86.39	$86.40	$86.40
7 purchase totals =	$739.96		$824.4417	$824.44	$824.40	$824.50