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	$39.69	7.651%	$42.7267	$42.73	$42.75	$42.70
Purchase #2	$206.69	7.415%	$222.0161	$222.02	$222.00	$222.00
Purchase #3	$133.38	10.221%	$147.0128	$147.01	$147.00	$147.00
Purchase #4	$160.48	3.654%	$166.3439	$166.34	$166.35	$166.30
Purchase #5	$208.75	11.659%	$233.0882	$233.09	$233.10	$233.10
Purchase #6	$145.81	10.381%	$160.9465	$160.95	$160.95	$160.90
Purchase #7	$114.37	3.712%	$118.6154	$118.62	$118.60	$118.60
7 purchase totals =	$1,009.17		$1,090.7496	$1,090.76	$1,090.75	$1,090.60