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	$136.90	3.236%	$141.3301	$141.33	$141.35	$141.30
Purchase #2	$88.78	12.432%	$99.8171	$99.82	$99.80	$99.80
Purchase #3	$183.61	4.681%	$192.2048	$192.20	$192.20	$192.20
Purchase #4	$222.56	8.266%	$240.9568	$240.96	$240.95	$241.00
Purchase #5	$106.82	5.421%	$112.6107	$112.61	$112.60	$112.60
Purchase #6	$220.65	7.552%	$237.3135	$237.31	$237.30	$237.30
Purchase #7	$236.73	7.124%	$253.5946	$253.59	$253.60	$253.60
7 purchase totals =	$1,196.05		$1,277.8276	$1,277.82	$1,277.80	$1,277.80