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	$79.48	3.670%	$82.3969	$82.40	$82.40	$82.40
Purchase #2	$212.92	11.284%	$236.9459	$236.95	$236.95	$236.90
Purchase #3	$111.82	7.637%	$120.3597	$120.36	$120.35	$120.40
Purchase #4	$203.67	3.855%	$211.5215	$211.52	$211.50	$211.50
Purchase #5	$40.85	5.281%	$43.0073	$43.01	$43.00	$43.00
Purchase #6	$213.72	4.550%	$223.4443	$223.44	$223.45	$223.40
Purchase #7	$7.61	3.610%	$7.8847	$7.88	$7.90	$7.90
7 purchase totals =	$870.07		$925.5603	$925.56	$925.55	$925.50