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	$200.87	11.267%	$223.502	$223.50	$223.50	$223.50
Purchase #2	$19.68	4.713%	$20.6075	$20.61	$20.60	$20.60
Purchase #3	$169.96	10.525%	$187.8483	$187.85	$187.85	$187.80
Purchase #4	$5.90	7.240%	$6.3272	$6.33	$6.35	$6.30
Purchase #5	$123.25	10.573%	$136.2812	$136.28	$136.30	$136.30
Purchase #6	$67.76	4.658%	$70.9163	$70.92	$70.90	$70.90
Purchase #7	$24.54	13.188%	$27.7763	$27.78	$27.80	$27.80
7 purchase totals =	$611.96		$673.2588	$673.27	$673.30	$673.20