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	$74.96	5.228%	$78.8789	$78.88	$78.90	$78.90
Purchase #2	$245.81	12.639%	$276.8779	$276.88	$276.90	$276.90
Purchase #3	$22.97	11.281%	$25.5612	$25.56	$25.55	$25.60
Purchase #4	$206.84	11.643%	$230.9224	$230.92	$230.90	$230.90
Purchase #5	$71.50	13.394%	$81.0767	$81.08	$81.10	$81.10
Purchase #6	$163.79	5.543%	$172.8689	$172.87	$172.85	$172.90
Purchase #7	$80.34	11.726%	$89.7607	$89.76	$89.75	$89.80
7 purchase totals =	$866.21		$955.9467	$955.95	$955.95	$956.10