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	$247.46	10.844%	$274.2946	$274.29	$274.30	$274.30
Purchase #2	$35.72	7.175%	$38.2829	$38.28	$38.30	$38.30
Purchase #3	$155.70	4.150%	$162.1616	$162.16	$162.15	$162.20
Purchase #4	$248.41	8.815%	$270.3073	$270.31	$270.30	$270.30
Purchase #5	$210.25	6.400%	$223.706	$223.71	$223.70	$223.70
Purchase #6	$243.39	7.456%	$261.5372	$261.54	$261.55	$261.50
Purchase #7	$43.68	3.152%	$45.0568	$45.06	$45.05	$45.10
7 purchase totals =	$1,184.61		$1,275.3464	$1,275.35	$1,275.35	$1,275.40