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	$78.70	12.775%	$88.7539	$88.75	$88.75	$88.80
Purchase #2	$82.51	8.591%	$89.5984	$89.60	$89.60	$89.60
Purchase #3	$122.41	13.808%	$139.3124	$139.31	$139.30	$139.30
Purchase #4	$170.96	9.315%	$186.8849	$186.88	$186.90	$186.90
Purchase #5	$249.81	12.592%	$281.2661	$281.27	$281.25	$281.30
Purchase #6	$39.80	5.256%	$41.8919	$41.89	$41.90	$41.90
Purchase #7	$182.32	11.646%	$203.553	$203.55	$203.55	$203.60
7 purchase totals =	$926.51		$1,031.2606	$1,031.25	$1,031.25	$1,031.40