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	$36.33	12.550%	$40.8894	$40.89	$40.90	$40.90
Purchase #2	$11.56	13.137%	$13.0786	$13.08	$13.10	$13.10
Purchase #3	$226.99	8.301%	$245.8324	$245.83	$245.85	$245.80
Purchase #4	$38.34	12.183%	$43.011	$43.01	$43.00	$43.00
Purchase #5	$60.38	6.145%	$64.0904	$64.09	$64.10	$64.10
Purchase #6	$236.40	9.693%	$259.3143	$259.31	$259.30	$259.30
Purchase #7	$81.33	6.543%	$86.6514	$86.65	$86.65	$86.70
7 purchase totals =	$691.33		$752.8675	$752.86	$752.90	$752.90