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	$138.45	3.258%	$142.9607	$142.96	$142.95	$143.00
Purchase #2	$104.80	4.591%	$109.6114	$109.61	$109.60	$109.60
Purchase #3	$167.42	7.496%	$179.9698	$179.97	$179.95	$180.00
Purchase #4	$198.40	6.811%	$211.913	$211.91	$211.90	$211.90
Purchase #5	$78.91	11.260%	$87.7953	$87.80	$87.80	$87.80
Purchase #6	$89.89	13.168%	$101.7267	$101.73	$101.75	$101.70
Purchase #7	$137.42	3.820%	$142.6694	$142.67	$142.65	$142.70
7 purchase totals =	$915.29		$976.6463	$976.65	$976.60	$976.70