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	$154.54	8.448%	$167.5955	$167.60	$167.60	$167.60
Purchase #2	$131.57	7.827%	$141.868	$141.87	$141.85	$141.90
Purchase #3	$190.96	3.732%	$198.0866	$198.09	$198.10	$198.10
Purchase #4	$110.72	8.715%	$120.3692	$120.37	$120.35	$120.40
Purchase #5	$178.33	4.374%	$186.1302	$186.13	$186.15	$186.10
Purchase #6	$38.54	4.817%	$40.3965	$40.40	$40.40	$40.40
Purchase #7	$229.79	7.109%	$246.1258	$246.13	$246.15	$246.10
7 purchase totals =	$1,034.45		$1,100.5718	$1,100.59	$1,100.60	$1,100.60