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	$242.98	9.123%	$265.1471	$265.15	$265.15	$265.10
Purchase #2	$76.51	11.509%	$85.3155	$85.32	$85.30	$85.30
Purchase #3	$120.30	3.822%	$124.8979	$124.90	$124.90	$124.90
Purchase #4	$84.97	7.812%	$91.6079	$91.61	$91.60	$91.60
Purchase #5	$211.32	12.867%	$238.5105	$238.51	$238.50	$238.50
Purchase #6	$89.94	9.755%	$98.7136	$98.71	$98.70	$98.70
Purchase #7	$176.48	5.374%	$185.964	$185.96	$185.95	$186.00
7 purchase totals =	$1,002.50		$1,090.1565	$1,090.16	$1,090.10	$1,090.10