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	$129.87	4.337%	$135.5025	$135.50	$135.50	$135.50
Purchase #2	$37.81	12.220%	$42.4304	$42.43	$42.45	$42.40
Purchase #3	$63.61	12.539%	$71.5861	$71.59	$71.60	$71.60
Purchase #4	$71.46	10.192%	$78.7432	$78.74	$78.75	$78.70
Purchase #5	$89.71	9.205%	$97.9678	$97.97	$97.95	$98.00
Purchase #6	$13.33	9.291%	$14.5685	$14.57	$14.55	$14.60
Purchase #7	$59.52	9.753%	$65.325	$65.33	$65.35	$65.30
7 purchase totals =	$465.31		$506.1235	$506.13	$506.15	$506.10