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	$128.54	9.780%	$141.1112	$141.11	$141.10	$141.10
Purchase #2	$85.42	5.641%	$90.2385	$90.24	$90.25	$90.20
Purchase #3	$196.39	8.554%	$213.1892	$213.19	$213.20	$213.20
Purchase #4	$192.66	10.648%	$213.1744	$213.17	$213.15	$213.20
Purchase #5	$159.29	7.710%	$171.5713	$171.57	$171.55	$171.60
Purchase #6	$44.81	13.692%	$50.9454	$50.95	$50.95	$50.90
Purchase #7	$225.56	4.778%	$236.3373	$236.34	$236.35	$236.30
7 purchase totals =	$1,032.67		$1,116.5673	$1,116.57	$1,116.55	$1,116.50