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	$109.77	3.137%	$113.2135	$113.21	$113.20	$113.20
Purchase #2	$219.59	9.622%	$240.7189	$240.72	$240.70	$240.70
Purchase #3	$125.95	10.869%	$139.6395	$139.64	$139.65	$139.60
Purchase #4	$66.98	7.791%	$72.1984	$72.20	$72.20	$72.20
Purchase #5	$78.31	13.427%	$88.8247	$88.82	$88.80	$88.80
Purchase #6	$56.55	11.291%	$62.9351	$62.94	$62.95	$62.90
Purchase #7	$59.88	9.121%	$65.3417	$65.34	$65.35	$65.30
7 purchase totals =	$717.03		$782.8718	$782.87	$782.85	$782.70