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	$89.59	13.393%	$101.5888	$101.59	$101.60	$101.60
Purchase #2	$91.29	4.205%	$95.1287	$95.13	$95.15	$95.10
Purchase #3	$175.80	4.605%	$183.8956	$183.90	$183.90	$183.90
Purchase #4	$76.94	11.516%	$85.8004	$85.80	$85.80	$85.80
Purchase #5	$64.36	9.581%	$70.5263	$70.53	$70.55	$70.50
Purchase #6	$131.36	6.514%	$139.9168	$139.92	$139.90	$139.90
Purchase #7	$142.61	5.814%	$150.9013	$150.90	$150.90	$150.90
7 purchase totals =	$771.95		$827.7579	$827.77	$827.80	$827.70