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	$190.51	8.450%	$206.6081	$206.61	$206.60	$206.60
Purchase #2	$61.47	13.523%	$69.7826	$69.78	$69.80	$69.80
Purchase #3	$103.67	13.644%	$117.8147	$117.81	$117.80	$117.80
Purchase #4	$199.72	11.455%	$222.5979	$222.60	$222.60	$222.60
Purchase #5	$91.54	10.858%	$101.4794	$101.48	$101.50	$101.50
Purchase #6	$96.46	13.301%	$109.2901	$109.29	$109.30	$109.30
Purchase #7	$131.32	11.431%	$146.3312	$146.33	$146.35	$146.30
7 purchase totals =	$874.69		$973.9040	$973.90	$973.95	$973.90