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	$247.89	13.216%	$280.6511	$280.65	$280.65	$280.70
Purchase #2	$85.49	4.624%	$89.4431	$89.44	$89.45	$89.40
Purchase #3	$196.81	6.197%	$209.0063	$209.01	$209.00	$209.00
Purchase #4	$81.62	8.109%	$88.2386	$88.24	$88.25	$88.20
Purchase #5	$66.62	9.567%	$72.9935	$72.99	$73.00	$73.00
Purchase #6	$55.82	11.698%	$62.3498	$62.35	$62.35	$62.30
Purchase #7	$27.65	13.649%	$31.4239	$31.42	$31.40	$31.40
7 purchase totals =	$761.90		$834.1063	$834.10	$834.10	$834.00