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	$210.25	6.827%	$224.6038	$224.60	$224.60	$224.60
Purchase #2	$128.61	9.755%	$141.1559	$141.16	$141.15	$141.20
Purchase #3	$36.55	13.775%	$41.5848	$41.58	$41.60	$41.60
Purchase #4	$93.71	4.681%	$98.0966	$98.10	$98.10	$98.10
Purchase #5	$172.88	6.687%	$184.4405	$184.44	$184.45	$184.40
Purchase #6	$82.33	12.221%	$92.3915	$92.39	$92.40	$92.40
Purchase #7	$79.68	12.187%	$89.3906	$89.39	$89.40	$89.40
7 purchase totals =	$804.01		$871.6637	$871.66	$871.70	$871.70