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	$203.35	4.733%	$212.9746	$212.97	$212.95	$213.00
Purchase #2	$178.31	7.870%	$192.343	$192.34	$192.35	$192.30
Purchase #3	$82.89	7.376%	$89.004	$89.00	$89.00	$89.00
Purchase #4	$233.38	13.612%	$265.1477	$265.15	$265.15	$265.10
Purchase #5	$6.69	5.108%	$7.0317	$7.03	$7.05	$7.00
Purchase #6	$172.71	11.768%	$193.0345	$193.03	$193.05	$193.00
Purchase #7	$119.59	9.795%	$131.3038	$131.30	$131.30	$131.30
7 purchase totals =	$996.92		$1,090.8393	$1,090.82	$1,090.85	$1,090.70