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	$70.49	11.619%	$78.6802	$78.68	$78.70	$78.70
Purchase #2	$135.88	8.651%	$147.635	$147.64	$147.65	$147.60
Purchase #3	$224.27	8.322%	$242.9337	$242.93	$242.95	$242.90
Purchase #4	$61.91	8.840%	$67.3828	$67.38	$67.40	$67.40
Purchase #5	$81.55	9.143%	$89.0061	$89.01	$89.00	$89.00
Purchase #6	$93.30	7.724%	$100.5065	$100.51	$100.50	$100.50
Purchase #7	$25.96	4.767%	$27.1975	$27.20	$27.20	$27.20
7 purchase totals =	$693.36		$753.3418	$753.35	$753.40	$753.30