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	$77.73	3.679%	$80.5897	$80.59	$80.60	$80.60
Purchase #2	$72.29	9.137%	$78.8951	$78.90	$78.90	$78.90
Purchase #3	$103.96	11.595%	$116.0142	$116.01	$116.00	$116.00
Purchase #4	$210.85	3.297%	$217.8017	$217.80	$217.80	$217.80
Purchase #5	$188.90	11.792%	$211.1751	$211.18	$211.20	$211.20
Purchase #6	$58.61	4.645%	$61.3324	$61.33	$61.35	$61.30
Purchase #7	$245.43	6.414%	$261.1719	$261.17	$261.15	$261.20
7 purchase totals =	$957.77		$1,026.9801	$1,026.98	$1,027.00	$1,027.00