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	$238.77	6.168%	$253.4973	$253.50	$253.50	$253.50
Purchase #2	$124.76	9.756%	$136.9316	$136.93	$136.95	$136.90
Purchase #3	$80.36	12.220%	$90.18	$90.18	$90.20	$90.20
Purchase #4	$155.44	10.558%	$171.8514	$171.85	$171.85	$171.90
Purchase #5	$238.47	8.556%	$258.8735	$258.87	$258.85	$258.90
Purchase #6	$18.46	9.526%	$20.2185	$20.22	$20.20	$20.20
Purchase #7	$101.44	9.761%	$111.3416	$111.34	$111.35	$111.30
7 purchase totals =	$957.70		$1,042.8939	$1,042.89	$1,042.90	$1,042.90