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	$164.37	3.669%	$170.4007	$170.40	$170.40	$170.40
Purchase #2	$64.91	10.627%	$71.808	$71.81	$71.80	$71.80
Purchase #3	$130.41	6.665%	$139.1018	$139.10	$139.10	$139.10
Purchase #4	$52.91	12.428%	$59.4857	$59.49	$59.50	$59.50
Purchase #5	$88.59	12.419%	$99.592	$99.59	$99.60	$99.60
Purchase #6	$50.46	9.571%	$55.2895	$55.29	$55.30	$55.30
Purchase #7	$168.92	12.252%	$189.6161	$189.62	$189.60	$189.60
7 purchase totals =	$720.57		$785.2938	$785.30	$785.30	$785.30