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	$28.77	13.150%	$32.5533	$32.55	$32.55	$32.60
Purchase #2	$36.59	10.776%	$40.5329	$40.53	$40.55	$40.50
Purchase #3	$213.45	12.541%	$240.2188	$240.22	$240.20	$240.20
Purchase #4	$240.35	4.765%	$251.8027	$251.80	$251.80	$251.80
Purchase #5	$33.67	12.122%	$37.7515	$37.75	$37.75	$37.80
Purchase #6	$80.40	13.796%	$91.492	$91.49	$91.50	$91.50
Purchase #7	$57.40	11.582%	$64.0481	$64.05	$64.05	$64.00
7 purchase totals =	$690.63		$758.3993	$758.39	$758.40	$758.40