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	$137.61	13.541%	$156.2438	$156.24	$156.25	$156.20
Purchase #2	$223.75	3.634%	$231.8811	$231.88	$231.90	$231.90
Purchase #3	$147.33	13.531%	$167.2652	$167.27	$167.25	$167.30
Purchase #4	$124.32	5.673%	$131.3727	$131.37	$131.35	$131.40
Purchase #5	$82.31	9.117%	$89.8142	$89.81	$89.80	$89.80
Purchase #6	$124.35	7.355%	$133.4959	$133.50	$133.50	$133.50
Purchase #7	$103.84	12.850%	$117.1834	$117.18	$117.20	$117.20
7 purchase totals =	$943.51		$1,027.2563	$1,027.25	$1,027.25	$1,027.30