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	$250.63	3.722%	$259.9584	$259.96	$259.95	$260.00
Purchase #2	$92.59	11.172%	$102.9342	$102.93	$102.95	$102.90
Purchase #3	$231.82	4.782%	$242.9056	$242.91	$242.90	$242.90
Purchase #4	$117.27	12.290%	$131.6825	$131.68	$131.70	$131.70
Purchase #5	$26.47	12.502%	$29.7793	$29.78	$29.80	$29.80
Purchase #6	$37.55	6.799%	$40.103	$40.10	$40.10	$40.10
Purchase #7	$182.40	7.356%	$195.8173	$195.82	$195.80	$195.80
7 purchase totals =	$938.73		$1,003.1803	$1,003.18	$1,003.20	$1,003.20