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	$27.36	13.819%	$31.1409	$31.14	$31.15	$31.10
Purchase #2	$63.62	12.108%	$71.3231	$71.32	$71.30	$71.30
Purchase #3	$99.49	12.260%	$111.6875	$111.69	$111.70	$111.70
Purchase #4	$219.61	8.237%	$237.6993	$237.70	$237.70	$237.70
Purchase #5	$100.86	4.721%	$105.6216	$105.62	$105.60	$105.60
Purchase #6	$192.78	9.854%	$211.7765	$211.78	$211.80	$211.80
Purchase #7	$237.48	13.272%	$268.9983	$269.00	$269.00	$269.00
7 purchase totals =	$941.20		$1,038.2472	$1,038.25	$1,038.25	$1,038.20