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	$86.28	4.289%	$89.9805	$89.98	$90.00	$90.00
Purchase #2	$192.71	11.739%	$215.3322	$215.33	$215.35	$215.30
Purchase #3	$223.92	11.587%	$249.8656	$249.87	$249.85	$249.90
Purchase #4	$210.32	10.342%	$232.0713	$232.07	$232.05	$232.10
Purchase #5	$119.51	7.557%	$128.5414	$128.54	$128.55	$128.50
Purchase #6	$63.93	8.683%	$69.481	$69.48	$69.50	$69.50
Purchase #7	$145.67	13.673%	$165.5875	$165.59	$165.60	$165.60
7 purchase totals =	$1,042.34		$1,150.8595	$1,150.86	$1,150.90	$1,150.90