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	$158.35	6.302%	$168.3292	$168.33	$168.35	$168.30
Purchase #2	$153.48	7.643%	$165.2105	$165.21	$165.20	$165.20
Purchase #3	$148.58	13.438%	$168.5462	$168.55	$168.55	$168.50
Purchase #4	$102.50	6.532%	$109.1953	$109.20	$109.20	$109.20
Purchase #5	$182.61	11.774%	$204.1105	$204.11	$204.10	$204.10
Purchase #6	$30.55	5.266%	$32.1588	$32.16	$32.15	$32.20
Purchase #7	$102.95	13.350%	$116.6938	$116.69	$116.70	$116.70
7 purchase totals =	$879.02		$964.2443	$964.25	$964.25	$964.20