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	$71.31	12.851%	$80.474	$80.47	$80.45	$80.50
Purchase #2	$221.60	8.847%	$241.205	$241.21	$241.20	$241.20
Purchase #3	$135.93	4.374%	$141.8756	$141.88	$141.90	$141.90
Purchase #4	$69.95	11.579%	$78.0495	$78.05	$78.05	$78.00
Purchase #5	$169.55	3.282%	$175.1146	$175.11	$175.10	$175.10
Purchase #6	$232.86	4.465%	$243.2572	$243.26	$243.25	$243.30
Purchase #7	$131.53	10.713%	$145.6208	$145.62	$145.60	$145.60
7 purchase totals =	$1,032.73		$1,105.5967	$1,105.60	$1,105.55	$1,105.60