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	$19.78	5.743%	$20.916	$20.92	$20.90	$20.90
Purchase #2	$71.28	9.427%	$77.9996	$78.00	$78.00	$78.00
Purchase #3	$155.92	10.703%	$172.6081	$172.61	$172.60	$172.60
Purchase #4	$233.34	6.737%	$249.0601	$249.06	$249.05	$249.10
Purchase #5	$139.56	7.507%	$150.0368	$150.04	$150.05	$150.00
Purchase #6	$200.46	4.686%	$209.8536	$209.85	$209.85	$209.90
Purchase #7	$51.90	4.708%	$54.3435	$54.34	$54.35	$54.30
7 purchase totals =	$872.24		$934.8177	$934.82	$934.80	$934.80