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	$72.46	13.279%	$82.082	$82.08	$82.10	$82.10
Purchase #2	$198.45	10.633%	$219.5512	$219.55	$219.55	$219.60
Purchase #3	$58.50	4.491%	$61.1272	$61.13	$61.15	$61.10
Purchase #4	$245.78	11.541%	$274.1455	$274.15	$274.15	$274.10
Purchase #5	$240.95	12.435%	$270.9121	$270.91	$270.90	$270.90
Purchase #6	$109.54	9.356%	$119.7886	$119.79	$119.80	$119.80
Purchase #7	$102.48	10.619%	$113.3624	$113.36	$113.35	$113.40
7 purchase totals =	$1,028.16		$1,140.9690	$1,140.97	$1,141.00	$1,141.00