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	$111.86	10.713%	$123.8436	$123.84	$123.85	$123.80
Purchase #2	$174.27	9.269%	$190.4231	$190.42	$190.40	$190.40
Purchase #3	$233.52	13.199%	$264.3423	$264.34	$264.35	$264.30
Purchase #4	$58.89	9.288%	$64.3597	$64.36	$64.35	$64.40
Purchase #5	$215.51	7.324%	$231.294	$231.29	$231.30	$231.30
Purchase #6	$92.79	6.499%	$98.8204	$98.82	$98.80	$98.80
Purchase #7	$242.81	9.226%	$265.2117	$265.21	$265.20	$265.20
7 purchase totals =	$1,129.65		$1,238.2948	$1,238.28	$1,238.25	$1,238.20