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	$74.99	5.160%	$78.8595	$78.86	$78.85	$78.90
Purchase #2	$93.77	13.371%	$106.308	$106.31	$106.30	$106.30
Purchase #3	$123.63	10.581%	$136.7113	$136.71	$136.70	$136.70
Purchase #4	$211.69	10.293%	$233.4793	$233.48	$233.50	$233.50
Purchase #5	$114.37	12.430%	$128.5862	$128.59	$128.60	$128.60
Purchase #6	$150.54	11.756%	$168.2375	$168.24	$168.25	$168.20
Purchase #7	$241.50	3.511%	$249.9791	$249.98	$250.00	$250.00
7 purchase totals =	$1,010.49		$1,102.1609	$1,102.17	$1,102.20	$1,102.20