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	$137.48	6.162%	$145.9515	$145.95	$145.95	$146.00
Purchase #2	$83.86	7.157%	$89.8619	$89.86	$89.85	$89.90
Purchase #3	$95.40	13.669%	$108.4402	$108.44	$108.45	$108.40
Purchase #4	$126.86	11.403%	$141.3258	$141.33	$141.35	$141.30
Purchase #5	$76.49	11.782%	$85.5021	$85.50	$85.50	$85.50
Purchase #6	$45.69	10.199%	$50.3499	$50.35	$50.35	$50.30
Purchase #7	$131.79	12.152%	$147.8051	$147.81	$147.80	$147.80
7 purchase totals =	$697.57		$769.2365	$769.24	$769.25	$769.20