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	$235.70	4.146%	$245.4721	$245.47	$245.45	$245.50
Purchase #2	$209.33	10.645%	$231.6132	$231.61	$231.60	$231.60
Purchase #3	$78.97	12.872%	$89.135	$89.14	$89.15	$89.10
Purchase #4	$91.30	3.499%	$94.4946	$94.49	$94.50	$94.50
Purchase #5	$23.88	6.713%	$25.4831	$25.48	$25.50	$25.50
Purchase #6	$140.96	11.554%	$157.2465	$157.25	$157.25	$157.20
Purchase #7	$231.26	3.340%	$238.9841	$238.98	$239.00	$239.00
7 purchase totals =	$1,011.40		$1,082.4286	$1,082.42	$1,082.45	$1,082.40