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	$80.45	12.397%	$90.4234	$90.42	$90.40	$90.40
Purchase #2	$182.33	7.669%	$196.3129	$196.31	$196.30	$196.30
Purchase #3	$232.47	4.573%	$243.1009	$243.10	$243.10	$243.10
Purchase #4	$31.93	10.766%	$35.3676	$35.37	$35.35	$35.40
Purchase #5	$13.44	7.750%	$14.4816	$14.48	$14.50	$14.50
Purchase #6	$242.38	11.576%	$270.4379	$270.44	$270.45	$270.40
Purchase #7	$117.31	5.858%	$124.182	$124.18	$124.20	$124.20
7 purchase totals =	$900.31		$974.3063	$974.30	$974.30	$974.30