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	$91.80	12.254%	$103.0492	$103.05	$103.05	$103.00
Purchase #2	$167.88	10.503%	$185.5124	$185.51	$185.50	$185.50
Purchase #3	$114.99	11.666%	$128.4047	$128.40	$128.40	$128.40
Purchase #4	$97.57	8.688%	$106.0469	$106.05	$106.05	$106.00
Purchase #5	$146.82	4.741%	$153.7807	$153.78	$153.80	$153.80
Purchase #6	$203.75	9.350%	$222.8006	$222.80	$222.80	$222.80
Purchase #7	$72.88	7.489%	$78.338	$78.34	$78.35	$78.30
7 purchase totals =	$895.69		$977.9325	$977.93	$977.95	$977.80