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	$27.52	12.304%	$30.9061	$30.91	$30.90	$30.90
Purchase #2	$62.51	3.814%	$64.8941	$64.89	$64.90	$64.90
Purchase #3	$63.70	13.851%	$72.5231	$72.52	$72.50	$72.50
Purchase #4	$243.94	5.231%	$256.7005	$256.70	$256.70	$256.70
Purchase #5	$127.57	10.800%	$141.3476	$141.35	$141.35	$141.30
Purchase #6	$182.30	4.220%	$189.9931	$189.99	$190.00	$190.00
Purchase #7	$248.57	12.427%	$279.4598	$279.46	$279.45	$279.50
7 purchase totals =	$956.11		$1,035.8243	$1,035.82	$1,035.80	$1,035.80