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	$229.86	8.354%	$249.0625	$249.06	$249.05	$249.10
Purchase #2	$64.45	7.433%	$69.2406	$69.24	$69.25	$69.20
Purchase #3	$190.96	9.398%	$208.9064	$208.91	$208.90	$208.90
Purchase #4	$127.93	6.735%	$136.5461	$136.55	$136.55	$136.50
Purchase #5	$128.29	8.743%	$139.5064	$139.51	$139.50	$139.50
Purchase #6	$90.70	10.850%	$100.541	$100.54	$100.55	$100.50
Purchase #7	$170.75	10.385%	$188.4824	$188.48	$188.50	$188.50
7 purchase totals =	$1,002.94		$1,092.2854	$1,092.29	$1,092.30	$1,092.20