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	$71.72	8.796%	$78.0285	$78.03	$78.05	$78.00
Purchase #2	$62.75	3.379%	$64.8703	$64.87	$64.85	$64.90
Purchase #3	$154.91	9.624%	$169.8185	$169.82	$169.80	$169.80
Purchase #4	$65.80	6.490%	$70.0704	$70.07	$70.05	$70.10
Purchase #5	$203.83	10.475%	$225.1812	$225.18	$225.20	$225.20
Purchase #6	$33.46	6.219%	$35.5409	$35.54	$35.55	$35.50
Purchase #7	$247.38	6.450%	$263.336	$263.34	$263.35	$263.30
7 purchase totals =	$839.85		$906.8458	$906.85	$906.85	$906.80