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	$111.65	10.606%	$123.4916	$123.49	$123.50	$123.50
Purchase #2	$175.86	3.592%	$182.1769	$182.18	$182.20	$182.20
Purchase #3	$84.49	12.365%	$94.9372	$94.94	$94.95	$94.90
Purchase #4	$156.44	13.316%	$177.2716	$177.27	$177.25	$177.30
Purchase #5	$53.82	4.155%	$56.0562	$56.06	$56.05	$56.10
Purchase #6	$94.62	4.750%	$99.1145	$99.11	$99.10	$99.10
Purchase #7	$247.82	9.308%	$270.8871	$270.89	$270.90	$270.90
7 purchase totals =	$924.70		$1,003.9351	$1,003.94	$1,003.95	$1,004.00