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	$20.91	12.714%	$23.5685	$23.57	$23.55	$23.60
Purchase #2	$96.57	13.503%	$109.6098	$109.61	$109.60	$109.60
Purchase #3	$155.78	6.386%	$165.7281	$165.73	$165.75	$165.70
Purchase #4	$57.48	4.204%	$59.8965	$59.90	$59.90	$59.90
Purchase #5	$65.45	5.425%	$69.0007	$69.00	$69.00	$69.00
Purchase #6	$222.45	10.409%	$245.6048	$245.60	$245.60	$245.60
Purchase #7	$150.37	9.492%	$164.6431	$164.64	$164.65	$164.60
7 purchase totals =	$769.01		$838.0515	$838.05	$838.05	$838.00