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	$157.82	9.708%	$173.1412	$173.14	$173.15	$173.10
Purchase #2	$105.84	6.862%	$113.1027	$113.10	$113.10	$113.10
Purchase #3	$117.26	5.623%	$123.8535	$123.85	$123.85	$123.90
Purchase #4	$120.77	4.207%	$125.8508	$125.85	$125.85	$125.90
Purchase #5	$86.65	3.787%	$89.9314	$89.93	$89.95	$89.90
Purchase #6	$106.65	11.672%	$119.0982	$119.10	$119.10	$119.10
Purchase #7	$229.91	12.316%	$258.2257	$258.23	$258.25	$258.20
7 purchase totals =	$924.90		$1,003.2035	$1,003.20	$1,003.25	$1,003.20