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	$79.67	11.226%	$88.6138	$88.61	$88.60	$88.60
Purchase #2	$211.94	5.298%	$223.1686	$223.17	$223.15	$223.20
Purchase #3	$185.54	5.863%	$196.4182	$196.42	$196.40	$196.40
Purchase #4	$111.60	4.374%	$116.4814	$116.48	$116.50	$116.50
Purchase #5	$245.37	10.380%	$270.8394	$270.84	$270.85	$270.80
Purchase #6	$164.84	8.612%	$179.036	$179.04	$179.05	$179.00
Purchase #7	$225.88	10.582%	$249.7826	$249.78	$249.80	$249.80
7 purchase totals =	$1,224.84		$1,324.3400	$1,324.34	$1,324.35	$1,324.30