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	$49.47	11.581%	$55.1991	$55.20	$55.20	$55.20
Purchase #2	$73.71	11.264%	$82.0127	$82.01	$82.00	$82.00
Purchase #3	$38.48	11.588%	$42.9391	$42.94	$42.95	$42.90
Purchase #4	$154.38	6.758%	$164.813	$164.81	$164.80	$164.80
Purchase #5	$112.31	11.573%	$125.3076	$125.31	$125.30	$125.30
Purchase #6	$142.65	6.223%	$151.5271	$151.53	$151.55	$151.50
Purchase #7	$197.52	3.388%	$204.212	$204.21	$204.20	$204.20
7 purchase totals =	$768.52		$826.0106	$826.01	$826.00	$825.90