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	$125.83	10.763%	$139.3731	$139.37	$139.35	$139.40
Purchase #2	$178.54	5.507%	$188.3722	$188.37	$188.35	$188.40
Purchase #3	$232.95	7.459%	$250.3257	$250.33	$250.35	$250.30
Purchase #4	$213.60	11.864%	$238.9415	$238.94	$238.95	$238.90
Purchase #5	$151.48	10.533%	$167.4354	$167.44	$167.45	$167.40
Purchase #6	$125.90	4.467%	$131.524	$131.52	$131.50	$131.50
Purchase #7	$140.80	5.288%	$148.2455	$148.25	$148.25	$148.20
7 purchase totals =	$1,169.10		$1,264.2174	$1,264.22	$1,264.20	$1,264.10