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	$224.48	10.524%	$248.1043	$248.10	$248.10	$248.10
Purchase #2	$169.69	11.644%	$189.4487	$189.45	$189.45	$189.40
Purchase #3	$59.75	7.803%	$64.4123	$64.41	$64.40	$64.40
Purchase #4	$242.87	9.227%	$265.2796	$265.28	$265.30	$265.30
Purchase #5	$158.64	3.695%	$164.5017	$164.50	$164.50	$164.50
Purchase #6	$216.33	6.142%	$229.617	$229.62	$229.60	$229.60
Purchase #7	$131.36	6.753%	$140.2307	$140.23	$140.25	$140.20
7 purchase totals =	$1,203.12		$1,301.5943	$1,301.59	$1,301.60	$1,301.50