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	$67.96	8.756%	$73.9106	$73.91	$73.90	$73.90
Purchase #2	$34.38	4.527%	$35.9364	$35.94	$35.95	$35.90
Purchase #3	$196.27	10.641%	$217.1551	$217.16	$217.15	$217.20
Purchase #4	$245.47	3.468%	$253.9829	$253.98	$254.00	$254.00
Purchase #5	$135.79	11.384%	$151.2483	$151.25	$151.25	$151.20
Purchase #6	$116.47	12.860%	$131.448	$131.45	$131.45	$131.40
Purchase #7	$60.25	10.144%	$66.3618	$66.36	$66.35	$66.40
7 purchase totals =	$856.59		$930.0431	$930.05	$930.05	$930.00