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	$21.30	4.204%	$22.1955	$22.20	$22.20	$22.20
Purchase #2	$39.63	7.825%	$42.731	$42.73	$42.75	$42.70
Purchase #3	$142.43	9.737%	$156.2984	$156.30	$156.30	$156.30
Purchase #4	$239.51	6.189%	$254.3333	$254.33	$254.35	$254.30
Purchase #5	$153.34	7.250%	$164.4572	$164.46	$164.45	$164.50
Purchase #6	$24.48	11.229%	$27.2289	$27.23	$27.25	$27.20
Purchase #7	$178.63	9.761%	$196.0661	$196.07	$196.05	$196.10
7 purchase totals =	$799.32		$863.3104	$863.32	$863.35	$863.30