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	$29.66	6.355%	$31.5449	$31.54	$31.55	$31.50
Purchase #2	$225.56	10.857%	$250.049	$250.05	$250.05	$250.00
Purchase #3	$122.36	3.410%	$126.5325	$126.53	$126.55	$126.50
Purchase #4	$69.27	8.689%	$75.2889	$75.29	$75.30	$75.30
Purchase #5	$238.61	6.312%	$253.6711	$253.67	$253.65	$253.70
Purchase #6	$180.98	10.585%	$200.1367	$200.14	$200.15	$200.10
Purchase #7	$53.37	11.552%	$59.5353	$59.54	$59.55	$59.50
7 purchase totals =	$919.81		$996.7584	$996.76	$996.80	$996.60