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	$102.95	10.518%	$113.7783	$113.78	$113.80	$113.80
Purchase #2	$203.52	9.234%	$222.313	$222.31	$222.30	$222.30
Purchase #3	$201.25	7.524%	$216.3921	$216.39	$216.40	$216.40
Purchase #4	$82.37	8.777%	$89.5996	$89.60	$89.60	$89.60
Purchase #5	$105.95	12.149%	$118.8219	$118.82	$118.80	$118.80
Purchase #6	$187.93	9.850%	$206.4411	$206.44	$206.45	$206.40
Purchase #7	$31.75	12.442%	$35.7003	$35.70	$35.70	$35.70
7 purchase totals =	$915.72		$1,003.0463	$1,003.04	$1,003.05	$1,003.00