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	$179.82	4.655%	$188.1906	$188.19	$188.20	$188.20
Purchase #2	$150.83	6.316%	$160.3564	$160.36	$160.35	$160.40
Purchase #3	$59.82	7.636%	$64.3879	$64.39	$64.40	$64.40
Purchase #4	$75.83	13.819%	$86.3089	$86.31	$86.30	$86.30
Purchase #5	$211.92	6.713%	$226.1462	$226.15	$226.15	$226.10
Purchase #6	$51.94	4.649%	$54.3547	$54.35	$54.35	$54.40
Purchase #7	$146.35	11.342%	$162.949	$162.95	$162.95	$162.90
7 purchase totals =	$876.51		$942.6937	$942.70	$942.70	$942.70