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	$234.94	5.681%	$248.2869	$248.29	$248.30	$248.30
Purchase #2	$136.69	4.111%	$142.3093	$142.31	$142.30	$142.30
Purchase #3	$108.64	3.311%	$112.2371	$112.24	$112.25	$112.20
Purchase #4	$163.69	6.839%	$174.8848	$174.88	$174.90	$174.90
Purchase #5	$36.82	12.467%	$41.4103	$41.41	$41.40	$41.40
Purchase #6	$119.48	11.752%	$133.5213	$133.52	$133.50	$133.50
Purchase #7	$168.25	6.651%	$179.4403	$179.44	$179.45	$179.40
7 purchase totals =	$968.51		$1,032.0900	$1,032.09	$1,032.10	$1,032.00