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	$171.79	8.188%	$185.8562	$185.86	$185.85	$185.90
Purchase #2	$106.64	9.373%	$116.6354	$116.64	$116.65	$116.60
Purchase #3	$166.99	12.398%	$187.6934	$187.69	$187.70	$187.70
Purchase #4	$28.25	12.255%	$31.712	$31.71	$31.70	$31.70
Purchase #5	$53.70	7.816%	$57.8972	$57.90	$57.90	$57.90
Purchase #6	$250.25	10.267%	$275.9432	$275.94	$275.95	$275.90
Purchase #7	$75.36	9.774%	$82.7257	$82.73	$82.75	$82.70
7 purchase totals =	$852.98		$938.4631	$938.47	$938.50	$938.40