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	$29.54	5.732%	$31.2332	$31.23	$31.25	$31.20
Purchase #2	$191.66	10.692%	$212.1523	$212.15	$212.15	$212.20
Purchase #3	$50.31	6.119%	$53.3885	$53.39	$53.40	$53.40
Purchase #4	$30.82	8.475%	$33.432	$33.43	$33.45	$33.40
Purchase #5	$245.50	7.353%	$263.5516	$263.55	$263.55	$263.60
Purchase #6	$134.82	8.202%	$145.8779	$145.88	$145.90	$145.90
Purchase #7	$153.69	7.702%	$165.5272	$165.53	$165.55	$165.50
7 purchase totals =	$836.34		$905.1627	$905.16	$905.25	$905.20