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	$242.61	11.294%	$270.0104	$270.01	$270.00	$270.00
Purchase #2	$140.47	5.112%	$147.6508	$147.65	$147.65	$147.70
Purchase #3	$126.61	9.804%	$139.0228	$139.02	$139.00	$139.00
Purchase #4	$191.72	9.308%	$209.5653	$209.57	$209.55	$209.60
Purchase #5	$157.63	4.582%	$164.8526	$164.85	$164.85	$164.90
Purchase #6	$26.68	11.861%	$29.8445	$29.84	$29.85	$29.80
Purchase #7	$38.60	8.482%	$41.8741	$41.87	$41.85	$41.90
7 purchase totals =	$924.32		$1,002.8205	$1,002.81	$1,002.75	$1,002.90