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	$74.60	5.398%	$78.6269	$78.63	$78.65	$78.60
Purchase #2	$193.37	13.188%	$218.8716	$218.87	$218.85	$218.90
Purchase #3	$107.42	5.814%	$113.6654	$113.67	$113.65	$113.70
Purchase #4	$90.88	5.572%	$95.9438	$95.94	$95.95	$95.90
Purchase #5	$200.76	7.184%	$215.1826	$215.18	$215.20	$215.20
Purchase #6	$54.90	12.279%	$61.6412	$61.64	$61.65	$61.60
Purchase #7	$63.39	6.451%	$67.4793	$67.48	$67.50	$67.50
7 purchase totals =	$785.32		$851.4108	$851.41	$851.45	$851.40