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	$131.70	7.290%	$141.3009	$141.30	$141.30	$141.30
Purchase #2	$40.88	9.401%	$44.7231	$44.72	$44.70	$44.70
Purchase #3	$83.38	8.658%	$90.599	$90.60	$90.60	$90.60
Purchase #4	$45.72	11.437%	$50.949	$50.95	$50.95	$50.90
Purchase #5	$234.72	10.196%	$258.6521	$258.65	$258.65	$258.70
Purchase #6	$40.64	4.873%	$42.6204	$42.62	$42.60	$42.60
Purchase #7	$210.60	4.366%	$219.7948	$219.79	$219.80	$219.80
7 purchase totals =	$787.64		$848.6393	$848.63	$848.60	$848.60