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	$183.91	9.138%	$200.7157	$200.72	$200.70	$200.70
Purchase #2	$112.87	4.400%	$117.8363	$117.84	$117.85	$117.80
Purchase #3	$93.80	12.527%	$105.5503	$105.55	$105.55	$105.60
Purchase #4	$52.67	12.724%	$59.3717	$59.37	$59.35	$59.40
Purchase #5	$108.34	3.404%	$112.0279	$112.03	$112.05	$112.00
Purchase #6	$113.37	6.588%	$120.8388	$120.84	$120.85	$120.80
Purchase #7	$221.42	4.846%	$232.15	$232.15	$232.15	$232.20
7 purchase totals =	$886.38		$948.4907	$948.50	$948.50	$948.50