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	$6.57	9.114%	$7.1688	$7.17	$7.15	$7.20
Purchase #2	$59.55	8.614%	$64.6796	$64.68	$64.70	$64.70
Purchase #3	$81.30	11.114%	$90.3357	$90.34	$90.35	$90.30
Purchase #4	$30.29	13.716%	$34.4446	$34.44	$34.45	$34.40
Purchase #5	$232.82	12.782%	$262.5791	$262.58	$262.60	$262.60
Purchase #6	$70.96	6.415%	$75.5121	$75.51	$75.50	$75.50
Purchase #7	$117.86	11.669%	$131.6131	$131.61	$131.60	$131.60
7 purchase totals =	$599.35		$666.3330	$666.33	$666.35	$666.30