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	$185.82	9.195%	$202.9061	$202.91	$202.90	$202.90
Purchase #2	$30.94	7.126%	$33.1448	$33.14	$33.15	$33.10
Purchase #3	$96.82	3.409%	$100.1206	$100.12	$100.10	$100.10
Purchase #4	$192.76	10.618%	$213.2273	$213.23	$213.25	$213.20
Purchase #5	$168.61	10.807%	$186.8317	$186.83	$186.85	$186.80
Purchase #6	$201.82	7.113%	$216.1755	$216.18	$216.20	$216.20
Purchase #7	$130.47	5.475%	$137.6132	$137.61	$137.60	$137.60
7 purchase totals =	$1,007.24		$1,090.0192	$1,090.02	$1,090.05	$1,089.90