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	$102.31	3.166%	$105.5491	$105.55	$105.55	$105.50
Purchase #2	$38.50	5.131%	$40.4754	$40.48	$40.50	$40.50
Purchase #3	$157.90	13.706%	$179.5418	$179.54	$179.55	$179.50
Purchase #4	$133.89	4.830%	$140.3569	$140.36	$140.35	$140.40
Purchase #5	$119.64	7.600%	$128.7326	$128.73	$128.75	$128.70
Purchase #6	$62.95	3.172%	$64.9468	$64.95	$64.95	$64.90
Purchase #7	$73.92	6.226%	$78.5223	$78.52	$78.50	$78.50
7 purchase totals =	$689.11		$738.1249	$738.13	$738.15	$738.00