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	$51.45	12.400%	$57.8298	$57.83	$57.85	$57.80
Purchase #2	$221.34	6.793%	$236.3756	$236.38	$236.40	$236.40
Purchase #3	$124.59	5.506%	$131.4499	$131.45	$131.45	$131.40
Purchase #4	$161.36	13.117%	$182.5256	$182.53	$182.55	$182.50
Purchase #5	$148.25	8.190%	$160.3917	$160.39	$160.40	$160.40
Purchase #6	$75.54	10.255%	$83.2866	$83.29	$83.30	$83.30
Purchase #7	$133.54	5.181%	$140.4587	$140.46	$140.45	$140.50
7 purchase totals =	$916.07		$992.3179	$992.33	$992.40	$992.30