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	$126.31	8.417%	$136.9415	$136.94	$136.95	$136.90
Purchase #2	$83.37	4.252%	$86.9149	$86.91	$86.90	$86.90
Purchase #3	$5.66	11.831%	$6.3296	$6.33	$6.35	$6.30
Purchase #4	$86.71	11.741%	$96.8906	$96.89	$96.90	$96.90
Purchase #5	$93.63	12.670%	$105.4929	$105.49	$105.50	$105.50
Purchase #6	$78.42	4.196%	$81.7105	$81.71	$81.70	$81.70
Purchase #7	$32.99	12.863%	$37.2335	$37.23	$37.25	$37.20
7 purchase totals =	$507.09		$551.5135	$551.50	$551.55	$551.40