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	$41.94	4.654%	$43.8919	$43.89	$43.90	$43.90
Purchase #2	$167.26	12.748%	$188.5823	$188.58	$188.60	$188.60
Purchase #3	$91.72	12.664%	$103.3354	$103.34	$103.35	$103.30
Purchase #4	$104.40	12.624%	$117.5795	$117.58	$117.60	$117.60
Purchase #5	$26.87	6.220%	$28.5413	$28.54	$28.55	$28.50
Purchase #6	$200.44	4.829%	$210.1192	$210.12	$210.10	$210.10
Purchase #7	$63.46	12.164%	$71.1793	$71.18	$71.20	$71.20
7 purchase totals =	$696.09		$763.2289	$763.23	$763.30	$763.20