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	$52.79	9.542%	$57.8272	$57.83	$57.85	$57.80
Purchase #2	$76.46	11.364%	$85.1489	$85.15	$85.15	$85.10
Purchase #3	$72.43	4.190%	$75.4648	$75.46	$75.45	$75.50
Purchase #4	$82.79	4.737%	$86.7118	$86.71	$86.70	$86.70
Purchase #5	$249.33	8.141%	$269.628	$269.63	$269.65	$269.60
Purchase #6	$20.70	13.841%	$23.5651	$23.57	$23.55	$23.60
Purchase #7	$210.99	5.476%	$222.5438	$222.54	$222.55	$222.50
7 purchase totals =	$765.49		$820.8896	$820.89	$820.90	$820.80