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	$248.96	10.194%	$274.339	$274.34	$274.35	$274.30
Purchase #2	$239.92	4.434%	$250.5581	$250.56	$250.55	$250.60
Purchase #3	$145.69	7.276%	$156.2904	$156.29	$156.30	$156.30
Purchase #4	$213.96	4.466%	$223.5155	$223.52	$223.50	$223.50
Purchase #5	$182.32	9.866%	$200.3077	$200.31	$200.30	$200.30
Purchase #6	$44.40	11.317%	$49.4247	$49.42	$49.40	$49.40
Purchase #7	$25.59	6.652%	$27.2922	$27.29	$27.30	$27.30
7 purchase totals =	$1,100.84		$1,181.7276	$1,181.73	$1,181.70	$1,181.70