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	$42.35	6.632%	$45.1587	$45.16	$45.15	$45.20
Purchase #2	$198.63	9.818%	$218.1315	$218.13	$218.15	$218.10
Purchase #3	$116.83	9.701%	$128.1637	$128.16	$128.15	$128.20
Purchase #4	$25.84	7.848%	$27.8679	$27.87	$27.85	$27.90
Purchase #5	$114.48	3.366%	$118.3334	$118.33	$118.35	$118.30
Purchase #6	$148.26	9.446%	$162.2646	$162.26	$162.25	$162.30
Purchase #7	$181.81	4.643%	$190.2514	$190.25	$190.25	$190.30
7 purchase totals =	$828.20		$890.1712	$890.16	$890.15	$890.30