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	$203.71	6.189%	$216.3176	$216.32	$216.30	$216.30
Purchase #2	$109.47	6.794%	$116.9074	$116.91	$116.90	$116.90
Purchase #3	$63.84	11.724%	$71.3246	$71.32	$71.30	$71.30
Purchase #4	$110.52	9.165%	$120.6492	$120.65	$120.65	$120.60
Purchase #5	$205.46	5.541%	$216.8445	$216.84	$216.85	$216.80
Purchase #6	$227.81	8.202%	$246.495	$246.50	$246.50	$246.50
Purchase #7	$83.53	10.728%	$92.4911	$92.49	$92.50	$92.50
7 purchase totals =	$1,004.34		$1,081.0294	$1,081.03	$1,081.00	$1,080.90