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	$81.29	9.497%	$89.0101	$89.01	$89.00	$89.00
Purchase #2	$140.32	5.457%	$147.9773	$147.98	$148.00	$148.00
Purchase #3	$6.49	13.812%	$7.3864	$7.39	$7.40	$7.40
Purchase #4	$34.78	9.155%	$37.9641	$37.96	$37.95	$38.00
Purchase #5	$81.27	5.861%	$86.0332	$86.03	$86.05	$86.00
Purchase #6	$85.87	6.563%	$91.5056	$91.51	$91.50	$91.50
Purchase #7	$5.77	10.797%	$6.393	$6.39	$6.40	$6.40
7 purchase totals =	$435.79		$466.2697	$466.27	$466.30	$466.30