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	$117.91	5.477%	$124.3679	$124.37	$124.35	$124.40
Purchase #2	$111.89	6.300%	$118.9391	$118.94	$118.95	$118.90
Purchase #3	$141.85	7.562%	$152.5767	$152.58	$152.60	$152.60
Purchase #4	$62.35	12.755%	$70.3027	$70.30	$70.30	$70.30
Purchase #5	$42.80	5.175%	$45.0149	$45.01	$45.00	$45.00
Purchase #6	$6.71	9.179%	$7.3259	$7.33	$7.35	$7.30
Purchase #7	$157.57	10.811%	$174.6049	$174.60	$174.60	$174.60
7 purchase totals =	$641.08		$693.1321	$693.13	$693.15	$693.10