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	$50.31	3.312%	$51.9763	$51.98	$52.00	$52.00
Purchase #2	$113.28	9.328%	$123.8468	$123.85	$123.85	$123.80
Purchase #3	$37.95	11.758%	$42.4122	$42.41	$42.40	$42.40
Purchase #4	$174.44	6.165%	$185.1942	$185.19	$185.20	$185.20
Purchase #5	$189.53	8.851%	$206.3053	$206.31	$206.30	$206.30
Purchase #6	$7.55	5.659%	$7.9773	$7.98	$8.00	$8.00
Purchase #7	$191.75	12.605%	$215.9201	$215.92	$215.90	$215.90
7 purchase totals =	$764.81		$833.6322	$833.64	$833.65	$833.60