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	$86.33	3.444%	$89.3032	$89.30	$89.30	$89.30
Purchase #2	$103.83	5.301%	$109.334	$109.33	$109.35	$109.30
Purchase #3	$239.76	12.347%	$269.3632	$269.36	$269.35	$269.40
Purchase #4	$37.96	5.322%	$39.9802	$39.98	$40.00	$40.00
Purchase #5	$6.40	4.483%	$6.6869	$6.69	$6.70	$6.70
Purchase #6	$69.91	5.340%	$73.6432	$73.64	$73.65	$73.60
Purchase #7	$99.91	5.567%	$105.472	$105.47	$105.45	$105.50
7 purchase totals =	$644.10		$693.7827	$693.77	$693.80	$693.80